diff --git a/go.mod b/go.mod
index 9d099b9..95e67d9 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,5 @@
 module github.com/emmansun/gmsm
 
 go 1.14
+
+require golang.org/x/crypto v0.0.0-20201221181555-eec23a3978ad
diff --git a/sm2/p256_asm.go b/sm2/p256_asm.go
index c9bd82e..1e26bb8 100644
--- a/sm2/p256_asm.go
+++ b/sm2/p256_asm.go
@@ -446,7 +446,7 @@ func boothW6(in uint) (int, int) {
 	return int(d), int(s & 1)
 }
 
-// table[i][j] = (2^(6*i))*j*G mod P
+// table[i][j] = (2^(6*i))*(j+1)*G mod P
 func initTable() {
 	p256Precomputed = new([43][32 * 8]uint64)
 
diff --git a/sm2/sm2.go b/sm2/sm2.go
index 7175463..2e2db1b 100644
--- a/sm2/sm2.go
+++ b/sm2/sm2.go
@@ -38,7 +38,7 @@ type combinedMult interface {
 	CombinedMult(bigX, bigY *big.Int, baseScalar, scalar []byte) (x, y *big.Int)
 }
 
-// PrivateKey represents an ECDSA private key.
+// PrivateKey represents an ECDSA SM2 private key.
 type PrivateKey struct {
 	ecdsa.PrivateKey
 }
@@ -76,6 +76,15 @@ func (mode pointMarshalMode) mashal(curve elliptic.Curve, x, y *big.Int) []byte
 
 var defaultEncrypterOpts = EncrypterOpts{MarshalUncompressed}
 
+// FromECPrivateKey convert an ecdsa private key to SM2 private key
+func (priv *PrivateKey) FromECPrivateKey(key *ecdsa.PrivateKey) (*PrivateKey, error) {
+	if key.Curve != P256() {
+		return nil, errors.New("It's NOT a sm2 curve private key")
+	}
+	priv.PrivateKey = *key
+	return priv, nil
+}
+
 // Sign signs digest with priv, reading randomness from rand. The opts argument
 // is not currently used but, in keeping with the crypto.Signer interface,
 // should be the hash function used to digest the message.
diff --git a/smx509/cert_pool.go b/smx509/cert_pool.go
new file mode 100644
index 0000000..a53f718
--- /dev/null
+++ b/smx509/cert_pool.go
@@ -0,0 +1,155 @@
+package smx509
+
+import (
+	"encoding/pem"
+	"errors"
+	"runtime"
+)
+
+// CertPool is a set of certificates.
+type CertPool struct {
+	bySubjectKeyId map[string][]int
+	byName         map[string][]int
+	certs          []*Certificate
+}
+
+// NewCertPool returns a new, empty CertPool.
+func NewCertPool() *CertPool {
+	return &CertPool{
+		bySubjectKeyId: make(map[string][]int),
+		byName:         make(map[string][]int),
+	}
+}
+
+func (s *CertPool) copy() *CertPool {
+	p := &CertPool{
+		bySubjectKeyId: make(map[string][]int, len(s.bySubjectKeyId)),
+		byName:         make(map[string][]int, len(s.byName)),
+		certs:          make([]*Certificate, len(s.certs)),
+	}
+	for k, v := range s.bySubjectKeyId {
+		indexes := make([]int, len(v))
+		copy(indexes, v)
+		p.bySubjectKeyId[k] = indexes
+	}
+	for k, v := range s.byName {
+		indexes := make([]int, len(v))
+		copy(indexes, v)
+		p.byName[k] = indexes
+	}
+	copy(p.certs, s.certs)
+	return p
+}
+
+// SystemCertPool returns a copy of the system cert pool.
+//
+// Any mutations to the returned pool are not written to disk and do
+// not affect any other pool returned by SystemCertPool.
+//
+// New changes in the system cert pool might not be reflected
+// in subsequent calls.
+func SystemCertPool() (*CertPool, error) {
+	if runtime.GOOS == "windows" {
+		// Issue 16736, 18609:
+		return nil, errors.New("crypto/x509: system root pool is not available on Windows")
+	}
+
+	if sysRoots := systemRootsPool(); sysRoots != nil {
+		return sysRoots.copy(), nil
+	}
+
+	return loadSystemRoots()
+}
+
+// findPotentialParents returns the indexes of certificates in s which might
+// have signed cert. The caller must not modify the returned slice.
+func (s *CertPool) findPotentialParents(cert *Certificate) []int {
+	if s == nil {
+		return nil
+	}
+
+	var candidates []int
+	if len(cert.AuthorityKeyId) > 0 {
+		candidates = s.bySubjectKeyId[string(cert.AuthorityKeyId)]
+	}
+	if len(candidates) == 0 {
+		candidates = s.byName[string(cert.RawIssuer)]
+	}
+	return candidates
+}
+
+func (s *CertPool) contains(cert *Certificate) bool {
+	if s == nil {
+		return false
+	}
+
+	candidates := s.byName[string(cert.RawSubject)]
+	for _, c := range candidates {
+		if s.certs[c].Equal(cert) {
+			return true
+		}
+	}
+
+	return false
+}
+
+// AddCert adds a certificate to a pool.
+func (s *CertPool) AddCert(cert *Certificate) {
+	if cert == nil {
+		panic("adding nil Certificate to CertPool")
+	}
+
+	// Check that the certificate isn't being added twice.
+	if s.contains(cert) {
+		return
+	}
+
+	n := len(s.certs)
+	s.certs = append(s.certs, cert)
+
+	if len(cert.SubjectKeyId) > 0 {
+		keyId := string(cert.SubjectKeyId)
+		s.bySubjectKeyId[keyId] = append(s.bySubjectKeyId[keyId], n)
+	}
+	name := string(cert.RawSubject)
+	s.byName[name] = append(s.byName[name], n)
+}
+
+// AppendCertsFromPEM attempts to parse a series of PEM encoded certificates.
+// It appends any certificates found to s and reports whether any certificates
+// were successfully parsed.
+//
+// On many Linux systems, /etc/ssl/cert.pem will contain the system wide set
+// of root CAs in a format suitable for this function.
+func (s *CertPool) AppendCertsFromPEM(pemCerts []byte) (ok bool) {
+	for len(pemCerts) > 0 {
+		var block *pem.Block
+		block, pemCerts = pem.Decode(pemCerts)
+		if block == nil {
+			break
+		}
+		if block.Type != "CERTIFICATE" || len(block.Headers) != 0 {
+			continue
+		}
+
+		cert, err := ParseCertificate(block.Bytes)
+		if err != nil {
+			continue
+		}
+
+		s.AddCert(cert)
+		ok = true
+	}
+
+	return
+}
+
+// Subjects returns a list of the DER-encoded subjects of
+// all of the certificates in the pool.
+func (s *CertPool) Subjects() [][]byte {
+	res := make([][]byte, len(s.certs))
+	for i, c := range s.certs {
+		res[i] = c.RawSubject
+	}
+	return res
+}
diff --git a/smx509/pkcs8.go b/smx509/pkcs8.go
new file mode 100644
index 0000000..13e5861
--- /dev/null
+++ b/smx509/pkcs8.go
@@ -0,0 +1,99 @@
+package smx509
+
+import (
+	"crypto/ecdsa"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/asn1"
+	"errors"
+
+	"github.com/emmansun/gmsm/sm2"
+)
+
+// pkcs8 reflects an ASN.1, PKCS#8 PrivateKey. See
+// ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-8/pkcs-8v1_2.asn
+// and RFC 5208.
+type pkcs8 struct {
+	Version    int
+	Algo       pkix.AlgorithmIdentifier
+	PrivateKey []byte
+	// optional attributes omitted.
+}
+
+// ParsePKCS8PrivateKey parses an unencrypted private key in PKCS#8, ASN.1 DER form.
+//
+// It returns a *rsa.PrivateKey, a *ecdsa.PrivateKey, or a ed25519.PrivateKey.
+// More types might be supported in the future.
+//
+// This kind of key is commonly encoded in PEM blocks of type "PRIVATE KEY".
+func ParsePKCS8PrivateKey(der []byte) (key interface{}, err error) {
+	var privKey pkcs8
+	if _, err := asn1.Unmarshal(der, &privKey); err != nil {
+		if _, err := asn1.Unmarshal(der, &ecPrivateKey{}); err == nil {
+			return nil, errors.New("x509: failed to parse private key (use ParseECPrivateKey instead for this key format)")
+		}
+		if _, err := asn1.Unmarshal(der, &pkcs1PrivateKey{}); err == nil {
+			return nil, errors.New("x509: failed to parse private key (use ParsePKCS1PrivateKey instead for this key format)")
+		}
+		return nil, err
+	}
+	if !privKey.Algo.Algorithm.Equal(oidPublicKeyECDSA) {
+		return x509.ParsePKCS8PrivateKey(der)
+	}
+	bytes := privKey.Algo.Parameters.FullBytes
+	namedCurveOID := new(asn1.ObjectIdentifier)
+	if _, err := asn1.Unmarshal(bytes, namedCurveOID); err != nil {
+		namedCurveOID = nil
+	}
+	ecKey, err := parseECPrivateKey(namedCurveOID, privKey.PrivateKey)
+	if err != nil {
+		return nil, errors.New("x509: failed to parse EC private key embedded in PKCS#8: " + err.Error())
+	}
+	if namedCurveOID.Equal(oidNamedCurveP256SM2) {
+		key, err = new(sm2.PrivateKey).FromECPrivateKey(ecKey)
+	} else {
+		key = ecKey
+	}
+	return key, nil
+}
+
+// MarshalPKCS8PrivateKey converts a private key to PKCS#8, ASN.1 DER form.
+//
+// The following key types are currently supported: *rsa.PrivateKey, *ecdsa.PrivateKey
+// and ed25519.PrivateKey. Unsupported key types result in an error.
+//
+// This kind of key is commonly encoded in PEM blocks of type "PRIVATE KEY".
+func MarshalPKCS8PrivateKey(key interface{}) ([]byte, error) {
+	switch k := key.(type) {
+	case *ecdsa.PrivateKey:
+		return marshalPKCS8ECPrivateKey(k)
+	case *sm2.PrivateKey:
+		return marshalPKCS8ECPrivateKey(&k.PrivateKey)
+	}
+	return x509.MarshalPKCS8PrivateKey(key)
+}
+
+func marshalPKCS8ECPrivateKey(k *ecdsa.PrivateKey) ([]byte, error) {
+	var privKey pkcs8
+	oid, ok := oidFromNamedCurve(k.Curve)
+	if !ok {
+		return nil, errors.New("x509: unknown curve while marshaling to PKCS#8")
+	}
+
+	oidBytes, err := asn1.Marshal(oid)
+	if err != nil {
+		return nil, errors.New("x509: failed to marshal curve OID: " + err.Error())
+	}
+
+	privKey.Algo = pkix.AlgorithmIdentifier{
+		Algorithm: oidPublicKeyECDSA,
+		Parameters: asn1.RawValue{
+			FullBytes: oidBytes,
+		},
+	}
+
+	if privKey.PrivateKey, err = marshalECPrivateKeyWithOID(k, nil); err != nil {
+		return nil, errors.New("x509: failed to marshal EC private key while building PKCS#8: " + err.Error())
+	}
+	return asn1.Marshal(privKey)
+}
diff --git a/smx509/pkcs8_test.go b/smx509/pkcs8_test.go
new file mode 100644
index 0000000..46c4491
--- /dev/null
+++ b/smx509/pkcs8_test.go
@@ -0,0 +1,157 @@
+package smx509
+
+import (
+	"bytes"
+	"crypto/ecdsa"
+	"crypto/ed25519"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/rsa"
+	"encoding/hex"
+	"fmt"
+	"reflect"
+	"strings"
+	"testing"
+
+	"github.com/emmansun/gmsm/sm2"
+)
+
+// Generated using:
+//   openssl genrsa 1024 | openssl pkcs8 -topk8 -nocrypt
+var pkcs8RSAPrivateKeyHex = `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`
+
+// Generated using:
+//   openssl ecparam -genkey -name secp224r1 | openssl pkcs8 -topk8 -nocrypt
+var pkcs8P224PrivateKeyHex = `3078020100301006072a8648ce3d020106052b810400210461305f020101041cca3d72b3e88fed2684576dad9b80a9180363a5424986900e3abcab3fa13c033a0004f8f2a6372872a4e61263ed893afb919576a4cacfecd6c081a2cbc76873cf4ba8530703c6042b3a00e2205087e87d2435d2e339e25702fae1`
+
+// Generated using:
+//   openssl ecparam -genkey -name secp256r1 | openssl pkcs8 -topk8 -nocrypt
+var pkcs8P256PrivateKeyHex = `308187020100301306072a8648ce3d020106082a8648ce3d030107046d306b0201010420dad6b2f49ca774c36d8ae9517e935226f667c929498f0343d2424d0b9b591b43a14403420004b9c9b90095476afe7b860d8bd43568cab7bcb2eed7b8bf2fa0ce1762dd20b04193f859d2d782b1e4cbfd48492f1f533113a6804903f292258513837f07fda735`
+
+var pkcs8SM2P256PrivateKeyHex = `308187020100301306072a8648ce3d020106082a811ccf5501822d046d306b0201010420b26da57ba53004ddcd387ad46a361b51b308481f2327d47fb10c5fb3a8c86b92a144034200040d5365bfdbdc564c5b0eda0a85ddbd753821a709de90efe0666ba2544766acf1100ac0484d166842011da5cd6139e53dedb99ce37cea9edf4941628066e861bf`
+
+// Generated using:
+//   openssl ecparam -genkey -name secp384r1 | openssl pkcs8 -topk8 -nocrypt
+var pkcs8P384PrivateKeyHex = `3081b6020100301006072a8648ce3d020106052b8104002204819e30819b02010104309bf832f6aaaeacb78ce47ffb15e6fd0fd48683ae79df6eca39bfb8e33829ac94aa29d08911568684c2264a08a4ceb679a164036200049070ad4ed993c7770d700e9f6dc2baa83f63dd165b5507f98e8ff29b5d2e78ccbe05c8ddc955dbf0f7497e8222cfa49314fe4e269459f8e880147f70d785e530f2939e4bf9f838325bb1a80ad4cf59272ae0e5efe9a9dc33d874492596304bd3`
+
+// Generated using:
+//   openssl ecparam -genkey -name secp521r1 | openssl pkcs8 -topk8 -nocrypt
+//
+// Note that OpenSSL will truncate the private key if it can (i.e. it emits it
+// like an integer, even though it's an OCTET STRING field). Thus if you
+// regenerate this you may, randomly, find that it's a byte shorter than
+// expected and the Go test will fail to recreate it exactly.
+var pkcs8P521PrivateKeyHex = `3081ee020100301006072a8648ce3d020106052b810400230481d63081d3020101044200cfe0b87113a205cf291bb9a8cd1a74ac6c7b2ebb8199aaa9a5010d8b8012276fa3c22ac913369fa61beec2a3b8b4516bc049bde4fb3b745ac11b56ab23ac52e361a1818903818600040138f75acdd03fbafa4f047a8e4b272ba9d555c667962b76f6f232911a5786a0964e5edea6bd21a6f8725720958de049c6e3e6661c1c91b227cebee916c0319ed6ca003db0a3206d372229baf9dd25d868bf81140a518114803ce40c1855074d68c4e9dab9e65efba7064c703b400f1767f217dac82715ac1f6d88c74baf47a7971de4ea`
+
+// From RFC 8410, Section 7.
+var pkcs8Ed25519PrivateKeyHex = `302e020100300506032b657004220420d4ee72dbf913584ad5b6d8f1f769f8ad3afe7c28cbf1d4fbe097a88f44755842`
+
+func TestPKCS8(t *testing.T) {
+	tests := []struct {
+		name    string
+		keyHex  string
+		keyType reflect.Type
+		curve   elliptic.Curve
+	}{
+		{
+			name:    "RSA private key",
+			keyHex:  pkcs8RSAPrivateKeyHex,
+			keyType: reflect.TypeOf(&rsa.PrivateKey{}),
+		},
+		{
+			name:    "P-224 private key",
+			keyHex:  pkcs8P224PrivateKeyHex,
+			keyType: reflect.TypeOf(&ecdsa.PrivateKey{}),
+			curve:   elliptic.P224(),
+		},
+		{
+			name:    "P-256 private key",
+			keyHex:  pkcs8P256PrivateKeyHex,
+			keyType: reflect.TypeOf(&ecdsa.PrivateKey{}),
+			curve:   elliptic.P256(),
+		},
+		{
+			name:    "SM2 P-256 private key",
+			keyHex:  pkcs8SM2P256PrivateKeyHex,
+			keyType: reflect.TypeOf(&sm2.PrivateKey{}),
+			curve:   sm2.P256(),
+		},
+		{
+			name:    "P-384 private key",
+			keyHex:  pkcs8P384PrivateKeyHex,
+			keyType: reflect.TypeOf(&ecdsa.PrivateKey{}),
+			curve:   elliptic.P384(),
+		},
+		{
+			name:    "P-521 private key",
+			keyHex:  pkcs8P521PrivateKeyHex,
+			keyType: reflect.TypeOf(&ecdsa.PrivateKey{}),
+			curve:   elliptic.P521(),
+		},
+		{
+			name:    "Ed25519 private key",
+			keyHex:  pkcs8Ed25519PrivateKeyHex,
+			keyType: reflect.TypeOf(ed25519.PrivateKey{}),
+		},
+	}
+
+	for _, test := range tests {
+		derBytes, err := hex.DecodeString(test.keyHex)
+		if err != nil {
+			t.Errorf("%s: failed to decode hex: %s", test.name, err)
+			continue
+		}
+		privKey, err := ParsePKCS8PrivateKey(derBytes)
+		if err != nil {
+			t.Errorf("%s: failed to decode PKCS#8: %s", test.name, err)
+			continue
+		}
+		if reflect.TypeOf(privKey) != test.keyType {
+			t.Errorf("%s: decoded PKCS#8 returned unexpected key type: %T", test.name, privKey)
+			continue
+		}
+		if ecKey, isEC := privKey.(*ecdsa.PrivateKey); isEC && ecKey.Curve != test.curve {
+			t.Errorf("%s: decoded PKCS#8 returned unexpected curve %#v", test.name, ecKey.Curve)
+			continue
+		}
+		reserialised, err := MarshalPKCS8PrivateKey(privKey)
+		if err != nil {
+			t.Errorf("%s: failed to marshal into PKCS#8: %s", test.name, err)
+			continue
+		}
+		if !bytes.Equal(derBytes, reserialised) {
+			t.Errorf("%s: marshaled PKCS#8 didn't match original: got %x, want %x", test.name, reserialised, derBytes)
+			continue
+		}
+	}
+}
+
+const hexPKCS8TestPKCS1Key = "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"
+const hexPKCS8TestECKey = "3081a40201010430bdb9839c08ee793d1157886a7a758a3c8b2a17a4df48f17ace57c72c56b4723cf21dcda21d4e1ad57ff034f19fcfd98ea00706052b81040022a16403620004feea808b5ee2429cfcce13c32160e1c960990bd050bb0fdf7222f3decd0a55008e32a6aa3c9062051c4cba92a7a3b178b24567412d43cdd2f882fa5addddd726fe3e208d2c26d733a773a597abb749714df7256ead5105fa6e7b3650de236b50"
+
+var pkcs8MismatchKeyTests = []struct {
+	hexKey        string
+	errorContains string
+}{
+	{hexKey: hexPKCS8TestECKey, errorContains: "use ParseECPrivateKey instead"},
+	{hexKey: hexPKCS8TestPKCS1Key, errorContains: "use ParsePKCS1PrivateKey instead"},
+}
+
+func TestPKCS8MismatchKeyFormat(t *testing.T) {
+	for i, test := range pkcs8MismatchKeyTests {
+		derBytes, _ := hex.DecodeString(test.hexKey)
+		_, err := ParsePKCS8PrivateKey(derBytes)
+		if !strings.Contains(err.Error(), test.errorContains) {
+			t.Errorf("#%d: expected error containing %q, got %s", i, test.errorContains, err)
+		}
+	}
+}
+
+func TestMarshalPKCS8SM2PrivateKey(t *testing.T) {
+	priv, _ := sm2.GenerateKey(rand.Reader)
+	res, err := MarshalPKCS8PrivateKey(priv)
+	if err != nil {
+		t.Fatalf("%v\n", err)
+	}
+	fmt.Printf("%s\n", hex.EncodeToString(res))
+}
diff --git a/smx509/root.go b/smx509/root.go
new file mode 100644
index 0000000..f779bee
--- /dev/null
+++ b/smx509/root.go
@@ -0,0 +1,21 @@
+package smx509
+
+import "sync"
+
+var (
+	once           sync.Once
+	systemRoots    *CertPool
+	systemRootsErr error
+)
+
+func systemRootsPool() *CertPool {
+	once.Do(initSystemRoots)
+	return systemRoots
+}
+
+func initSystemRoots() {
+	systemRoots, systemRootsErr = loadSystemRoots()
+	if systemRootsErr != nil {
+		systemRoots = nil
+	}
+}
diff --git a/smx509/root_aix.go b/smx509/root_aix.go
new file mode 100644
index 0000000..ecac5c9
--- /dev/null
+++ b/smx509/root_aix.go
@@ -0,0 +1,6 @@
+package smx509
+
+// Possible certificate files; stop after finding one.
+var certFiles = []string{
+	"/var/ssl/certs/ca-bundle.crt",
+}
diff --git a/smx509/root_bsd.go b/smx509/root_bsd.go
new file mode 100644
index 0000000..55a9ea9
--- /dev/null
+++ b/smx509/root_bsd.go
@@ -0,0 +1,11 @@
+// +build dragonfly freebsd netbsd openbsd
+
+package smx509
+
+// Possible certificate files; stop after finding one.
+var certFiles = []string{
+	"/usr/local/etc/ssl/cert.pem",            // FreeBSD
+	"/etc/ssl/cert.pem",                      // OpenBSD
+	"/usr/local/share/certs/ca-root-nss.crt", // DragonFly
+	"/etc/openssl/certs/ca-certificates.crt", // NetBSD
+}
diff --git a/smx509/root_js.go b/smx509/root_js.go
new file mode 100644
index 0000000..148fd40
--- /dev/null
+++ b/smx509/root_js.go
@@ -0,0 +1,6 @@
+// +build js,wasm
+
+package smx509
+
+// Possible certificate files; stop after finding one.
+var certFiles = []string{}
diff --git a/smx509/root_linux.go b/smx509/root_linux.go
new file mode 100644
index 0000000..a0c2287
--- /dev/null
+++ b/smx509/root_linux.go
@@ -0,0 +1,11 @@
+package smx509
+
+// Possible certificate files; stop after finding one.
+var certFiles = []string{
+	"/etc/ssl/certs/ca-certificates.crt",                // Debian/Ubuntu/Gentoo etc.
+	"/etc/pki/tls/certs/ca-bundle.crt",                  // Fedora/RHEL 6
+	"/etc/ssl/ca-bundle.pem",                            // OpenSUSE
+	"/etc/pki/tls/cacert.pem",                           // OpenELEC
+	"/etc/pki/ca-trust/extracted/pem/tls-ca-bundle.pem", // CentOS/RHEL 7
+	"/etc/ssl/cert.pem",                                 // Alpine Linux
+}
diff --git a/smx509/root_plan9.go b/smx509/root_plan9.go
new file mode 100644
index 0000000..11c7487
--- /dev/null
+++ b/smx509/root_plan9.go
@@ -0,0 +1,36 @@
+// +build plan9
+
+package smx509
+
+import (
+	"io/ioutil"
+	"os"
+)
+
+// Possible certificate files; stop after finding one.
+var certFiles = []string{
+	"/sys/lib/tls/ca.pem",
+}
+
+func (c *Certificate) systemVerify(opts *VerifyOptions) (chains [][]*Certificate, err error) {
+	return nil, nil
+}
+
+func loadSystemRoots() (*CertPool, error) {
+	roots := NewCertPool()
+	var bestErr error
+	for _, file := range certFiles {
+		data, err := ioutil.ReadFile(file)
+		if err == nil {
+			roots.AppendCertsFromPEM(data)
+			return roots, nil
+		}
+		if bestErr == nil || (os.IsNotExist(bestErr) && !os.IsNotExist(err)) {
+			bestErr = err
+		}
+	}
+	if bestErr == nil {
+		return roots, nil
+	}
+	return nil, bestErr
+}
diff --git a/smx509/root_solaris.go b/smx509/root_solaris.go
new file mode 100644
index 0000000..97c22ef
--- /dev/null
+++ b/smx509/root_solaris.go
@@ -0,0 +1,8 @@
+package smx509
+
+// Possible certificate files; stop after finding one.
+var certFiles = []string{
+	"/etc/certs/ca-certificates.crt",     // Solaris 11.2+
+	"/etc/ssl/certs/ca-certificates.crt", // Joyent SmartOS
+	"/etc/ssl/cacert.pem",                // OmniOS
+}
diff --git a/smx509/root_unix.go b/smx509/root_unix.go
new file mode 100644
index 0000000..a6cbeeb
--- /dev/null
+++ b/smx509/root_unix.go
@@ -0,0 +1,85 @@
+// +build aix dragonfly freebsd js,wasm linux netbsd openbsd solaris
+
+package smx509
+
+import (
+	"io/ioutil"
+	"os"
+)
+
+// Possible directories with certificate files; stop after successfully
+// reading at least one file from a directory.
+var certDirectories = []string{
+	"/etc/ssl/certs",               // SLES10/SLES11, https://golang.org/issue/12139
+	"/system/etc/security/cacerts", // Android
+	"/usr/local/share/certs",       // FreeBSD
+	"/etc/pki/tls/certs",           // Fedora/RHEL
+	"/etc/openssl/certs",           // NetBSD
+	"/var/ssl/certs",               // AIX
+}
+
+const (
+	// certFileEnv is the environment variable which identifies where to locate
+	// the SSL certificate file. If set this overrides the system default.
+	certFileEnv = "SSL_CERT_FILE"
+
+	// certDirEnv is the environment variable which identifies which directory
+	// to check for SSL certificate files. If set this overrides the system default.
+	certDirEnv = "SSL_CERT_DIR"
+)
+
+func (c *Certificate) systemVerify(opts *VerifyOptions) (chains [][]*Certificate, err error) {
+	return nil, nil
+}
+
+func loadSystemRoots() (*CertPool, error) {
+	roots := NewCertPool()
+
+	files := certFiles
+	if f := os.Getenv(certFileEnv); f != "" {
+		files = []string{f}
+	}
+
+	var firstErr error
+	for _, file := range files {
+		data, err := ioutil.ReadFile(file)
+		if err == nil {
+			roots.AppendCertsFromPEM(data)
+			break
+		}
+		if firstErr == nil && !os.IsNotExist(err) {
+			firstErr = err
+		}
+	}
+
+	dirs := certDirectories
+	if d := os.Getenv(certDirEnv); d != "" {
+		dirs = []string{d}
+	}
+
+	for _, directory := range dirs {
+		fis, err := ioutil.ReadDir(directory)
+		if err != nil {
+			if firstErr == nil && !os.IsNotExist(err) {
+				firstErr = err
+			}
+			continue
+		}
+		rootsAdded := false
+		for _, fi := range fis {
+			data, err := ioutil.ReadFile(directory + "/" + fi.Name())
+			if err == nil && roots.AppendCertsFromPEM(data) {
+				rootsAdded = true
+			}
+		}
+		if rootsAdded {
+			return roots, nil
+		}
+	}
+
+	if len(roots.certs) > 0 || firstErr == nil {
+		return roots, nil
+	}
+
+	return nil, firstErr
+}
diff --git a/smx509/root_windows.go b/smx509/root_windows.go
new file mode 100644
index 0000000..5aa56a7
--- /dev/null
+++ b/smx509/root_windows.go
@@ -0,0 +1,303 @@
+package smx509
+
+import (
+	"crypto/x509"
+	"errors"
+	"syscall"
+	"unsafe"
+)
+
+// Creates a new *syscall.CertContext representing the leaf certificate in an in-memory
+// certificate store containing itself and all of the intermediate certificates specified
+// in the opts.Intermediates CertPool.
+//
+// A pointer to the in-memory store is available in the returned CertContext's Store field.
+// The store is automatically freed when the CertContext is freed using
+// syscall.CertFreeCertificateContext.
+func createStoreContext(leaf *Certificate, opts *VerifyOptions) (*syscall.CertContext, error) {
+	var storeCtx *syscall.CertContext
+
+	leafCtx, err := syscall.CertCreateCertificateContext(syscall.X509_ASN_ENCODING|syscall.PKCS_7_ASN_ENCODING, &leaf.Raw[0], uint32(len(leaf.Raw)))
+	if err != nil {
+		return nil, err
+	}
+	defer syscall.CertFreeCertificateContext(leafCtx)
+
+	handle, err := syscall.CertOpenStore(syscall.CERT_STORE_PROV_MEMORY, 0, 0, syscall.CERT_STORE_DEFER_CLOSE_UNTIL_LAST_FREE_FLAG, 0)
+	if err != nil {
+		return nil, err
+	}
+	defer syscall.CertCloseStore(handle, 0)
+
+	err = syscall.CertAddCertificateContextToStore(handle, leafCtx, syscall.CERT_STORE_ADD_ALWAYS, &storeCtx)
+	if err != nil {
+		return nil, err
+	}
+
+	if opts.Intermediates != nil {
+		for _, intermediate := range opts.Intermediates.certs {
+			ctx, err := syscall.CertCreateCertificateContext(syscall.X509_ASN_ENCODING|syscall.PKCS_7_ASN_ENCODING, &intermediate.Raw[0], uint32(len(intermediate.Raw)))
+			if err != nil {
+				return nil, err
+			}
+
+			err = syscall.CertAddCertificateContextToStore(handle, ctx, syscall.CERT_STORE_ADD_ALWAYS, nil)
+			syscall.CertFreeCertificateContext(ctx)
+			if err != nil {
+				return nil, err
+			}
+		}
+	}
+
+	return storeCtx, nil
+}
+
+// extractSimpleChain extracts the final certificate chain from a CertSimpleChain.
+func extractSimpleChain(simpleChain **syscall.CertSimpleChain, count int) (chain []*Certificate, err error) {
+	if simpleChain == nil || count == 0 {
+		return nil, errors.New("x509: invalid simple chain")
+	}
+
+	simpleChains := (*[1 << 20]*syscall.CertSimpleChain)(unsafe.Pointer(simpleChain))[:count:count]
+	lastChain := simpleChains[count-1]
+	elements := (*[1 << 20]*syscall.CertChainElement)(unsafe.Pointer(lastChain.Elements))[:lastChain.NumElements:lastChain.NumElements]
+	for i := 0; i < int(lastChain.NumElements); i++ {
+		// Copy the buf, since ParseCertificate does not create its own copy.
+		cert := elements[i].CertContext
+		encodedCert := (*[1 << 20]byte)(unsafe.Pointer(cert.EncodedCert))[:cert.Length:cert.Length]
+		buf := make([]byte, cert.Length)
+		copy(buf, encodedCert)
+		parsedCert, err := ParseCertificate(buf)
+		if err != nil {
+			return nil, err
+		}
+		chain = append(chain, parsedCert)
+	}
+
+	return chain, nil
+}
+
+// checkChainTrustStatus checks the trust status of the certificate chain, translating
+// any errors it finds into Go errors in the process.
+func checkChainTrustStatus(c *Certificate, chainCtx *syscall.CertChainContext) error {
+	if chainCtx.TrustStatus.ErrorStatus != syscall.CERT_TRUST_NO_ERROR {
+		status := chainCtx.TrustStatus.ErrorStatus
+		switch status {
+		case syscall.CERT_TRUST_IS_NOT_TIME_VALID:
+			return x509.CertificateInvalidError{&c.Certificate, x509.Expired, ""}
+		case syscall.CERT_TRUST_IS_NOT_VALID_FOR_USAGE:
+			return x509.CertificateInvalidError{&c.Certificate, x509.IncompatibleUsage, ""}
+		// TODO(filippo): surface more error statuses.
+		default:
+			return UnknownAuthorityError{c, nil, nil}
+		}
+	}
+	return nil
+}
+
+// checkChainSSLServerPolicy checks that the certificate chain in chainCtx is valid for
+// use as a certificate chain for a SSL/TLS server.
+func checkChainSSLServerPolicy(c *Certificate, chainCtx *syscall.CertChainContext, opts *VerifyOptions) error {
+	servernamep, err := syscall.UTF16PtrFromString(opts.DNSName)
+	if err != nil {
+		return err
+	}
+	sslPara := &syscall.SSLExtraCertChainPolicyPara{
+		AuthType:   syscall.AUTHTYPE_SERVER,
+		ServerName: servernamep,
+	}
+	sslPara.Size = uint32(unsafe.Sizeof(*sslPara))
+
+	para := &syscall.CertChainPolicyPara{
+		ExtraPolicyPara: (syscall.Pointer)(unsafe.Pointer(sslPara)),
+	}
+	para.Size = uint32(unsafe.Sizeof(*para))
+
+	status := syscall.CertChainPolicyStatus{}
+	err = syscall.CertVerifyCertificateChainPolicy(syscall.CERT_CHAIN_POLICY_SSL, chainCtx, para, &status)
+	if err != nil {
+		return err
+	}
+
+	// TODO(mkrautz): use the lChainIndex and lElementIndex fields
+	// of the CertChainPolicyStatus to provide proper context, instead
+	// using c.
+	if status.Error != 0 {
+		switch status.Error {
+		case syscall.CERT_E_EXPIRED:
+			return x509.CertificateInvalidError{&c.Certificate, x509.Expired, ""}
+		case syscall.CERT_E_CN_NO_MATCH:
+			return x509.HostnameError{&c.Certificate, opts.DNSName}
+		case syscall.CERT_E_UNTRUSTEDROOT:
+			return UnknownAuthorityError{c, nil, nil}
+		default:
+			return UnknownAuthorityError{c, nil, nil}
+		}
+	}
+
+	return nil
+}
+
+// windowsExtKeyUsageOIDs are the C NUL-terminated string representations of the
+// OIDs for use with the Windows API.
+var windowsExtKeyUsageOIDs = make(map[x509.ExtKeyUsage][]byte, len(extKeyUsageOIDs))
+
+func init() {
+	for _, eku := range extKeyUsageOIDs {
+		windowsExtKeyUsageOIDs[eku.extKeyUsage] = []byte(eku.oid.String() + "\x00")
+	}
+}
+
+// systemVerify is like Verify, except that it uses CryptoAPI calls
+// to build certificate chains and verify them.
+func (c *Certificate) systemVerify(opts *VerifyOptions) (chains [][]*Certificate, err error) {
+	storeCtx, err := createStoreContext(c, opts)
+	if err != nil {
+		return nil, err
+	}
+	defer syscall.CertFreeCertificateContext(storeCtx)
+
+	para := new(syscall.CertChainPara)
+	para.Size = uint32(unsafe.Sizeof(*para))
+
+	keyUsages := opts.KeyUsages
+	if len(keyUsages) == 0 {
+		keyUsages = []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth}
+	}
+	oids := make([]*byte, 0, len(keyUsages))
+	for _, eku := range keyUsages {
+		if eku == x509.ExtKeyUsageAny {
+			oids = nil
+			break
+		}
+		if oid, ok := windowsExtKeyUsageOIDs[eku]; ok {
+			oids = append(oids, &oid[0])
+		}
+		// Like the standard verifier, accept SGC EKUs as equivalent to ServerAuth.
+		if eku == x509.ExtKeyUsageServerAuth {
+			oids = append(oids, &syscall.OID_SERVER_GATED_CRYPTO[0])
+			oids = append(oids, &syscall.OID_SGC_NETSCAPE[0])
+		}
+	}
+	if oids != nil {
+		para.RequestedUsage.Type = syscall.USAGE_MATCH_TYPE_OR
+		para.RequestedUsage.Usage.Length = uint32(len(oids))
+		para.RequestedUsage.Usage.UsageIdentifiers = &oids[0]
+	} else {
+		para.RequestedUsage.Type = syscall.USAGE_MATCH_TYPE_AND
+		para.RequestedUsage.Usage.Length = 0
+		para.RequestedUsage.Usage.UsageIdentifiers = nil
+	}
+
+	var verifyTime *syscall.Filetime
+	if opts != nil && !opts.CurrentTime.IsZero() {
+		ft := syscall.NsecToFiletime(opts.CurrentTime.UnixNano())
+		verifyTime = &ft
+	}
+
+	// CertGetCertificateChain will traverse Windows's root stores
+	// in an attempt to build a verified certificate chain. Once
+	// it has found a verified chain, it stops. MSDN docs on
+	// CERT_CHAIN_CONTEXT:
+	//
+	//   When a CERT_CHAIN_CONTEXT is built, the first simple chain
+	//   begins with an end certificate and ends with a self-signed
+	//   certificate. If that self-signed certificate is not a root
+	//   or otherwise trusted certificate, an attempt is made to
+	//   build a new chain. CTLs are used to create the new chain
+	//   beginning with the self-signed certificate from the original
+	//   chain as the end certificate of the new chain. This process
+	//   continues building additional simple chains until the first
+	//   self-signed certificate is a trusted certificate or until
+	//   an additional simple chain cannot be built.
+	//
+	// The result is that we'll only get a single trusted chain to
+	// return to our caller.
+	var chainCtx *syscall.CertChainContext
+	err = syscall.CertGetCertificateChain(syscall.Handle(0), storeCtx, verifyTime, storeCtx.Store, para, 0, 0, &chainCtx)
+	if err != nil {
+		return nil, err
+	}
+	defer syscall.CertFreeCertificateChain(chainCtx)
+
+	err = checkChainTrustStatus(c, chainCtx)
+	if err != nil {
+		return nil, err
+	}
+
+	if opts != nil && len(opts.DNSName) > 0 {
+		err = checkChainSSLServerPolicy(c, chainCtx, opts)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	chain, err := extractSimpleChain(chainCtx.Chains, int(chainCtx.ChainCount))
+	if err != nil {
+		return nil, err
+	}
+	if len(chain) < 1 {
+		return nil, errors.New("x509: internal error: system verifier returned an empty chain")
+	}
+
+	// Mitigate CVE-2020-0601, where the Windows system verifier might be
+	// tricked into using custom curve parameters for a trusted root, by
+	// double-checking all ECDSA signatures. If the system was tricked into
+	// using spoofed parameters, the signature will be invalid for the correct
+	// ones we parsed. (We don't support custom curves ourselves.)
+	for i, parent := range chain[1:] {
+		if parent.PublicKeyAlgorithm != x509.ECDSA {
+			continue
+		}
+		if err := parent.CheckSignature(chain[i].SignatureAlgorithm,
+			chain[i].RawTBSCertificate, chain[i].Signature); err != nil {
+			return nil, err
+		}
+	}
+
+	return [][]*Certificate{chain}, nil
+}
+
+func loadSystemRoots() (*CertPool, error) {
+	// TODO: restore this functionality on Windows. We tried to do
+	// it in Go 1.8 but had to revert it. See Issue 18609.
+	// Returning (nil, nil) was the old behavior, prior to CL 30578.
+	// The if statement here avoids vet complaining about
+	// unreachable code below.
+	if true {
+		return nil, nil
+	}
+
+	const CRYPT_E_NOT_FOUND = 0x80092004
+
+	store, err := syscall.CertOpenSystemStore(0, syscall.StringToUTF16Ptr("ROOT"))
+	if err != nil {
+		return nil, err
+	}
+	defer syscall.CertCloseStore(store, 0)
+
+	roots := NewCertPool()
+	var cert *syscall.CertContext
+	for {
+		cert, err = syscall.CertEnumCertificatesInStore(store, cert)
+		if err != nil {
+			if errno, ok := err.(syscall.Errno); ok {
+				if errno == CRYPT_E_NOT_FOUND {
+					break
+				}
+			}
+			return nil, err
+		}
+		if cert == nil {
+			break
+		}
+		// Copy the buf, since ParseCertificate does not create its own copy.
+		buf := (*[1 << 20]byte)(unsafe.Pointer(cert.EncodedCert))[:cert.Length:cert.Length]
+		buf2 := make([]byte, cert.Length)
+		copy(buf2, buf)
+		if c, err := ParseCertificate(buf2); err == nil {
+			roots.AddCert(c)
+		}
+	}
+	return roots, nil
+}
diff --git a/smx509/sec1.go b/smx509/sec1.go
new file mode 100644
index 0000000..601980f
--- /dev/null
+++ b/smx509/sec1.go
@@ -0,0 +1,159 @@
+package smx509
+
+import (
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"encoding/asn1"
+	"errors"
+	"fmt"
+	"math/big"
+
+	"github.com/emmansun/gmsm/sm2"
+)
+
+// pkcs1PrivateKey is a structure which mirrors the PKCS#1 ASN.1 for an RSA private key.
+type pkcs1PrivateKey struct {
+	Version int
+	N       *big.Int
+	E       int
+	D       *big.Int
+	P       *big.Int
+	Q       *big.Int
+	// We ignore these values, if present, because rsa will calculate them.
+	Dp   *big.Int `asn1:"optional"`
+	Dq   *big.Int `asn1:"optional"`
+	Qinv *big.Int `asn1:"optional"`
+
+	AdditionalPrimes []pkcs1AdditionalRSAPrime `asn1:"optional,omitempty"`
+}
+
+type pkcs1AdditionalRSAPrime struct {
+	Prime *big.Int
+
+	// We ignore these values because rsa will calculate them.
+	Exp   *big.Int
+	Coeff *big.Int
+}
+
+const ecPrivKeyVersion = 1
+
+// ecPrivateKey reflects an ASN.1 Elliptic Curve Private Key Structure.
+// References:
+//   RFC 5915
+//   SEC1 - http://www.secg.org/sec1-v2.pdf
+// Per RFC 5915 the NamedCurveOID is marked as ASN.1 OPTIONAL, however in
+// most cases it is not.
+type ecPrivateKey struct {
+	Version       int
+	PrivateKey    []byte
+	NamedCurveOID asn1.ObjectIdentifier `asn1:"optional,explicit,tag:0"`
+	PublicKey     asn1.BitString        `asn1:"optional,explicit,tag:1"`
+}
+
+// ParseECPrivateKey parses an EC private key in SEC 1, ASN.1 DER form.
+//
+// This kind of key is commonly encoded in PEM blocks of type "EC PRIVATE KEY".
+func ParseECPrivateKey(der []byte) (*ecdsa.PrivateKey, error) {
+	return parseECPrivateKey(nil, der)
+}
+
+// ParseSM2PrivateKey parses an SM2 private key
+func ParseSM2PrivateKey(der []byte) (*sm2.PrivateKey, error) {
+	key, err := parseECPrivateKey(nil, der)
+	if err != nil {
+		return nil, err
+	}
+	return new(sm2.PrivateKey).FromECPrivateKey(key)
+}
+
+// MarshalECPrivateKey converts an EC private key to SEC 1, ASN.1 DER form.
+//
+// This kind of key is commonly encoded in PEM blocks of type "EC PRIVATE KEY".
+// For a more flexible key format which is not EC specific, use
+// MarshalPKCS8PrivateKey.
+func MarshalECPrivateKey(key *ecdsa.PrivateKey) ([]byte, error) {
+	oid, ok := oidFromNamedCurve(key.Curve)
+	if !ok {
+		return nil, errors.New("x509: unknown elliptic curve")
+	}
+
+	return marshalECPrivateKeyWithOID(key, oid)
+}
+
+// MarshalSM2PrivateKey convient method to marshal sm2 private key directly
+func MarshalSM2PrivateKey(key *sm2.PrivateKey) ([]byte, error) {
+	return MarshalECPrivateKey(&key.PrivateKey)
+}
+
+// marshalECPrivateKey marshals an EC private key into ASN.1, DER format and
+// sets the curve ID to the given OID, or omits it if OID is nil.
+func marshalECPrivateKeyWithOID(key *ecdsa.PrivateKey, oid asn1.ObjectIdentifier) ([]byte, error) {
+	privateKeyBytes := key.D.Bytes()
+	paddedPrivateKey := make([]byte, (key.Curve.Params().N.BitLen()+7)/8)
+	copy(paddedPrivateKey[len(paddedPrivateKey)-len(privateKeyBytes):], privateKeyBytes)
+
+	return asn1.Marshal(ecPrivateKey{
+		Version:       1,
+		PrivateKey:    paddedPrivateKey,
+		NamedCurveOID: oid,
+		PublicKey:     asn1.BitString{Bytes: elliptic.Marshal(key.Curve, key.X, key.Y)},
+	})
+}
+
+// parseECPrivateKey parses an ASN.1 Elliptic Curve Private Key Structure.
+// The OID for the named curve may be provided from another source (such as
+// the PKCS8 container) - if it is provided then use this instead of the OID
+// that may exist in the EC private key structure.
+func parseECPrivateKey(namedCurveOID *asn1.ObjectIdentifier, der []byte) (key *ecdsa.PrivateKey, err error) {
+	var privKey ecPrivateKey
+	if _, err := asn1.Unmarshal(der, &privKey); err != nil {
+		if _, err := asn1.Unmarshal(der, &pkcs8{}); err == nil {
+			return nil, errors.New("x509: failed to parse private key (use ParsePKCS8PrivateKey instead for this key format)")
+		}
+		if _, err := asn1.Unmarshal(der, &pkcs1PrivateKey{}); err == nil {
+			return nil, errors.New("x509: failed to parse private key (use ParsePKCS1PrivateKey instead for this key format)")
+		}
+		return nil, errors.New("x509: failed to parse EC private key: " + err.Error())
+	}
+	if privKey.Version != ecPrivKeyVersion {
+		return nil, fmt.Errorf("x509: unknown EC private key version %d", privKey.Version)
+	}
+
+	var curve elliptic.Curve
+	if namedCurveOID != nil {
+		curve = namedCurveFromOID(*namedCurveOID)
+	} else {
+		curve = namedCurveFromOID(privKey.NamedCurveOID)
+	}
+	if curve == nil {
+		return nil, errors.New("x509: unknown elliptic curve")
+	}
+
+	k := new(big.Int).SetBytes(privKey.PrivateKey)
+	curveOrder := curve.Params().N
+	if k.Cmp(curveOrder) >= 0 {
+		return nil, errors.New("x509: invalid elliptic curve private key value")
+	}
+	priv := new(ecdsa.PrivateKey)
+	priv.Curve = curve
+	priv.D = k
+
+	privateKey := make([]byte, (curveOrder.BitLen()+7)/8)
+
+	// Some private keys have leading zero padding. This is invalid
+	// according to [SEC1], but this code will ignore it.
+	for len(privKey.PrivateKey) > len(privateKey) {
+		if privKey.PrivateKey[0] != 0 {
+			return nil, errors.New("x509: invalid private key length")
+		}
+		privKey.PrivateKey = privKey.PrivateKey[1:]
+	}
+
+	// Some private keys remove all leading zeros, this is also invalid
+	// according to [SEC1] but since OpenSSL used to do this, we ignore
+	// this too.
+	copy(privateKey[len(privateKey)-len(privKey.PrivateKey):], privKey.PrivateKey)
+	priv.X, priv.Y = curve.ScalarBaseMult(privateKey)
+
+	return priv, nil
+}
diff --git a/smx509/sec1_test.go b/smx509/sec1_test.go
new file mode 100644
index 0000000..36cac6e
--- /dev/null
+++ b/smx509/sec1_test.go
@@ -0,0 +1,77 @@
+package smx509
+
+import (
+	"bytes"
+	"crypto/rand"
+	"encoding/hex"
+	"fmt"
+	"strings"
+	"testing"
+
+	"github.com/emmansun/gmsm/sm2"
+)
+
+var ecKeyTests = []struct {
+	derHex            string
+	shouldReserialize bool
+}{
+	// Generated using:
+	//   openssl ecparam -genkey -name secp384r1 -outform PEM
+	{"3081a40201010430bdb9839c08ee793d1157886a7a758a3c8b2a17a4df48f17ace57c72c56b4723cf21dcda21d4e1ad57ff034f19fcfd98ea00706052b81040022a16403620004feea808b5ee2429cfcce13c32160e1c960990bd050bb0fdf7222f3decd0a55008e32a6aa3c9062051c4cba92a7a3b178b24567412d43cdd2f882fa5addddd726fe3e208d2c26d733a773a597abb749714df7256ead5105fa6e7b3650de236b50", true},
+	// Generated using MarshalSM2PrivateKey
+	{"30770201010420857dd87970aab4328dad891c781e3b270742aa9cf5d3d3764efe77f6c3d6e33aa00a06082a811ccf5501822da14403420004ced963a5705a0490ff13dde893cbda6de61f41fcaf917a5b4007d30cdec46426bc39b9c18d15b2a68a64dc333f262e600b675856285b42296f24741ee6f562a0", true},
+	// This key was generated by GnuTLS and has illegal zero-padding of the
+	// private key. See https://golang.org/issues/13699.
+	{"3078020101042100f9f43a04b9bdc3ab01f53be6df80e7a7bc3eaf7b87fc24e630a4a0aa97633645a00a06082a8648ce3d030107a1440342000441a51bc318461b4c39a45048a16d4fc2a935b1ea7fe86e8c1fa219d6f2438f7c7fd62957d3442efb94b6a23eb0ea66dda663dc42f379cda6630b21b7888a5d3d", false},
+	// This was generated using an old version of OpenSSL and is missing a
+	// leading zero byte in the private key that should be present.
+	{"3081db0201010441607b4f985774ac21e633999794542e09312073480baa69550914d6d43d8414441e61b36650567901da714f94dffb3ce0e2575c31928a0997d51df5c440e983ca17a00706052b81040023a181890381860004001661557afedd7ac8d6b70e038e576558c626eb62edda36d29c3a1310277c11f67a8c6f949e5430a37dcfb95d902c1b5b5379c389873b9dd17be3bdb088a4774a7401072f830fb9a08d93bfa50a03dd3292ea07928724ddb915d831917a338f6b0aecfbc3cf5352c4a1295d356890c41c34116d29eeb93779aab9d9d78e2613437740f6", false},
+}
+
+func TestParseECPrivateKey(t *testing.T) {
+	for i, test := range ecKeyTests {
+		derBytes, _ := hex.DecodeString(test.derHex)
+		key, err := ParseECPrivateKey(derBytes)
+		if err != nil {
+			t.Fatalf("#%d: failed to decode EC private key: %s", i, err)
+		}
+		serialized, err := MarshalECPrivateKey(key)
+		if err != nil {
+			t.Fatalf("#%d: failed to encode EC private key: %s", i, err)
+		}
+		matches := bytes.Equal(serialized, derBytes)
+		if matches != test.shouldReserialize {
+			t.Fatalf("#%d: when serializing key: matches=%t, should match=%t: original %x, reserialized %x", i, matches, test.shouldReserialize, serialized, derBytes)
+		}
+	}
+}
+
+const hexECTestPKCS1Key = "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"
+const hexECTestPKCS8Key = "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"
+
+var ecMismatchKeyTests = []struct {
+	hexKey        string
+	errorContains string
+}{
+	{hexKey: hexECTestPKCS8Key, errorContains: "use ParsePKCS8PrivateKey instead"},
+	{hexKey: hexECTestPKCS1Key, errorContains: "use ParsePKCS1PrivateKey instead"},
+}
+
+func TestECMismatchKeyFormat(t *testing.T) {
+	for i, test := range ecMismatchKeyTests {
+		derBytes, _ := hex.DecodeString(test.hexKey)
+		_, err := ParseECPrivateKey(derBytes)
+		if !strings.Contains(err.Error(), test.errorContains) {
+			t.Errorf("#%d: expected error containing %q, got %s", i, test.errorContains, err)
+		}
+	}
+}
+
+func TestMarshalSM2PrivateKey(t *testing.T) {
+	priv, _ := sm2.GenerateKey(rand.Reader)
+	res, err := MarshalSM2PrivateKey(priv)
+	if err != nil {
+		t.Fatalf("%v\n", err)
+	}
+	fmt.Printf("%s\n", hex.EncodeToString(res))
+}
diff --git a/smx509/verify.go b/smx509/verify.go
new file mode 100644
index 0000000..52402ed
--- /dev/null
+++ b/smx509/verify.go
@@ -0,0 +1,984 @@
+package smx509
+
+import (
+	"bytes"
+	"crypto/x509"
+	"errors"
+	"fmt"
+	"net"
+	"net/url"
+	"os"
+	"reflect"
+	"runtime"
+	"strings"
+	"time"
+	"unicode/utf8"
+)
+
+// ignoreCN disables interpreting Common Name as a hostname. See issue 24151.
+var ignoreCN = strings.Contains(os.Getenv("GODEBUG"), "x509ignoreCN=1")
+
+// CertificateInvalidError results when an odd error occurs. Users of this
+// library probably want to handle all these errors uniformly.
+type CertificateInvalidError struct {
+	Cert   *Certificate
+	Reason x509.InvalidReason
+	Detail string
+}
+
+func (e CertificateInvalidError) Error() string {
+	switch e.Reason {
+	case x509.NotAuthorizedToSign:
+		return "x509: certificate is not authorized to sign other certificates"
+	case x509.Expired:
+		return "x509: certificate has expired or is not yet valid: " + e.Detail
+	case x509.CANotAuthorizedForThisName:
+		return "x509: a root or intermediate certificate is not authorized to sign for this name: " + e.Detail
+	case x509.CANotAuthorizedForExtKeyUsage:
+		return "x509: a root or intermediate certificate is not authorized for an extended key usage: " + e.Detail
+	case x509.TooManyIntermediates:
+		return "x509: too many intermediates for path length constraint"
+	case x509.IncompatibleUsage:
+		return "x509: certificate specifies an incompatible key usage"
+	case x509.NameMismatch:
+		return "x509: issuer name does not match subject from issuing certificate"
+	case x509.NameConstraintsWithoutSANs:
+		return "x509: issuer has name constraints but leaf doesn't have a SAN extension"
+	case x509.UnconstrainedName:
+		return "x509: issuer has name constraints but leaf contains unknown or unconstrained name: " + e.Detail
+	}
+	return "x509: unknown error"
+}
+
+// UnknownAuthorityError results when the certificate issuer is unknown
+type UnknownAuthorityError struct {
+	Cert *Certificate
+	// hintErr contains an error that may be helpful in determining why an
+	// authority wasn't found.
+	hintErr error
+	// hintCert contains a possible authority certificate that was rejected
+	// because of the error in hintErr.
+	hintCert *Certificate
+}
+
+func (e UnknownAuthorityError) Error() string {
+	s := "x509: certificate signed by unknown authority"
+	if e.hintErr != nil {
+		certName := e.hintCert.Subject.CommonName
+		if len(certName) == 0 {
+			if len(e.hintCert.Subject.Organization) > 0 {
+				certName = e.hintCert.Subject.Organization[0]
+			} else {
+				certName = "serial:" + e.hintCert.SerialNumber.String()
+			}
+		}
+		s += fmt.Sprintf(" (possibly because of %q while trying to verify candidate authority certificate %q)", e.hintErr, certName)
+	}
+	return s
+}
+
+// SystemRootsError results when we fail to load the system root certificates.
+type SystemRootsError struct {
+	Err error
+}
+
+func (se SystemRootsError) Error() string {
+	msg := "x509: failed to load system roots and no roots provided"
+	if se.Err != nil {
+		return msg + "; " + se.Err.Error()
+	}
+	return msg
+}
+
+// errNotParsed is returned when a certificate without ASN.1 contents is
+// verified. Platform-specific verification needs the ASN.1 contents.
+var errNotParsed = errors.New("x509: missing ASN.1 contents; use ParseCertificate")
+
+// VerifyOptions contains parameters for Certificate.Verify.
+type VerifyOptions struct {
+	// DNSName, if set, is checked against the leaf certificate with
+	// Certificate.VerifyHostname or the platform verifier.
+	DNSName string
+
+	// Intermediates is an optional pool of certificates that are not trust
+	// anchors, but can be used to form a chain from the leaf certificate to a
+	// root certificate.
+	Intermediates *CertPool
+	// Roots is the set of trusted root certificates the leaf certificate needs
+	// to chain up to. If nil, the system roots or the platform verifier are used.
+	Roots *CertPool
+
+	// CurrentTime is used to check the validity of all certificates in the
+	// chain. If zero, the current time is used.
+	CurrentTime time.Time
+
+	// KeyUsages specifies which Extended Key Usage values are acceptable. A
+	// chain is accepted if it allows any of the listed values. An empty list
+	// means ExtKeyUsageServerAuth. To accept any key usage, include ExtKeyUsageAny.
+	KeyUsages []x509.ExtKeyUsage
+
+	// MaxConstraintComparisions is the maximum number of comparisons to
+	// perform when checking a given certificate's name constraints. If
+	// zero, a sensible default is used. This limit prevents pathological
+	// certificates from consuming excessive amounts of CPU time when
+	// validating. It does not apply to the platform verifier.
+	MaxConstraintComparisions int
+}
+
+const (
+	leafCertificate = iota
+	intermediateCertificate
+	rootCertificate
+)
+
+// rfc2821Mailbox represents a “mailbox” (which is an email address to most
+// people) by breaking it into the “local” (i.e. before the '@') and “domain”
+// parts.
+type rfc2821Mailbox struct {
+	local, domain string
+}
+
+// parseRFC2821Mailbox parses an email address into local and domain parts,
+// based on the ABNF for a “Mailbox” from RFC 2821. According to RFC 5280,
+// Section 4.2.1.6 that's correct for an rfc822Name from a certificate: “The
+// format of an rfc822Name is a "Mailbox" as defined in RFC 2821, Section 4.1.2”.
+func parseRFC2821Mailbox(in string) (mailbox rfc2821Mailbox, ok bool) {
+	if len(in) == 0 {
+		return mailbox, false
+	}
+
+	localPartBytes := make([]byte, 0, len(in)/2)
+
+	if in[0] == '"' {
+		// Quoted-string = DQUOTE *qcontent DQUOTE
+		// non-whitespace-control = %d1-8 / %d11 / %d12 / %d14-31 / %d127
+		// qcontent = qtext / quoted-pair
+		// qtext = non-whitespace-control /
+		//         %d33 / %d35-91 / %d93-126
+		// quoted-pair = ("\" text) / obs-qp
+		// text = %d1-9 / %d11 / %d12 / %d14-127 / obs-text
+		//
+		// (Names beginning with “obs-” are the obsolete syntax from RFC 2822,
+		// Section 4. Since it has been 16 years, we no longer accept that.)
+		in = in[1:]
+	QuotedString:
+		for {
+			if len(in) == 0 {
+				return mailbox, false
+			}
+			c := in[0]
+			in = in[1:]
+
+			switch {
+			case c == '"':
+				break QuotedString
+
+			case c == '\\':
+				// quoted-pair
+				if len(in) == 0 {
+					return mailbox, false
+				}
+				if in[0] == 11 ||
+					in[0] == 12 ||
+					(1 <= in[0] && in[0] <= 9) ||
+					(14 <= in[0] && in[0] <= 127) {
+					localPartBytes = append(localPartBytes, in[0])
+					in = in[1:]
+				} else {
+					return mailbox, false
+				}
+
+			case c == 11 ||
+				c == 12 ||
+				// Space (char 32) is not allowed based on the
+				// BNF, but RFC 3696 gives an example that
+				// assumes that it is. Several “verified”
+				// errata continue to argue about this point.
+				// We choose to accept it.
+				c == 32 ||
+				c == 33 ||
+				c == 127 ||
+				(1 <= c && c <= 8) ||
+				(14 <= c && c <= 31) ||
+				(35 <= c && c <= 91) ||
+				(93 <= c && c <= 126):
+				// qtext
+				localPartBytes = append(localPartBytes, c)
+
+			default:
+				return mailbox, false
+			}
+		}
+	} else {
+		// Atom ("." Atom)*
+	NextChar:
+		for len(in) > 0 {
+			// atext from RFC 2822, Section 3.2.4
+			c := in[0]
+
+			switch {
+			case c == '\\':
+				// Examples given in RFC 3696 suggest that
+				// escaped characters can appear outside of a
+				// quoted string. Several “verified” errata
+				// continue to argue the point. We choose to
+				// accept it.
+				in = in[1:]
+				if len(in) == 0 {
+					return mailbox, false
+				}
+				fallthrough
+
+			case ('0' <= c && c <= '9') ||
+				('a' <= c && c <= 'z') ||
+				('A' <= c && c <= 'Z') ||
+				c == '!' || c == '#' || c == '$' || c == '%' ||
+				c == '&' || c == '\'' || c == '*' || c == '+' ||
+				c == '-' || c == '/' || c == '=' || c == '?' ||
+				c == '^' || c == '_' || c == '`' || c == '{' ||
+				c == '|' || c == '}' || c == '~' || c == '.':
+				localPartBytes = append(localPartBytes, in[0])
+				in = in[1:]
+
+			default:
+				break NextChar
+			}
+		}
+
+		if len(localPartBytes) == 0 {
+			return mailbox, false
+		}
+
+		// From RFC 3696, Section 3:
+		// “period (".") may also appear, but may not be used to start
+		// or end the local part, nor may two or more consecutive
+		// periods appear.”
+		twoDots := []byte{'.', '.'}
+		if localPartBytes[0] == '.' ||
+			localPartBytes[len(localPartBytes)-1] == '.' ||
+			bytes.Contains(localPartBytes, twoDots) {
+			return mailbox, false
+		}
+	}
+
+	if len(in) == 0 || in[0] != '@' {
+		return mailbox, false
+	}
+	in = in[1:]
+
+	// The RFC species a format for domains, but that's known to be
+	// violated in practice so we accept that anything after an '@' is the
+	// domain part.
+	if _, ok := domainToReverseLabels(in); !ok {
+		return mailbox, false
+	}
+
+	mailbox.local = string(localPartBytes)
+	mailbox.domain = in
+	return mailbox, true
+}
+
+// checkNameConstraints checks that c permits a child certificate to claim the
+// given name, of type nameType. The argument parsedName contains the parsed
+// form of name, suitable for passing to the match function. The total number
+// of comparisons is tracked in the given count and should not exceed the given
+// limit.
+func (c *Certificate) checkNameConstraints(count *int,
+	maxConstraintComparisons int,
+	nameType string,
+	name string,
+	parsedName interface{},
+	match func(parsedName, constraint interface{}) (match bool, err error),
+	permitted, excluded interface{}) error {
+
+	excludedValue := reflect.ValueOf(excluded)
+
+	*count += excludedValue.Len()
+	if *count > maxConstraintComparisons {
+		return CertificateInvalidError{c, x509.TooManyConstraints, ""}
+	}
+
+	for i := 0; i < excludedValue.Len(); i++ {
+		constraint := excludedValue.Index(i).Interface()
+		match, err := match(parsedName, constraint)
+		if err != nil {
+			return CertificateInvalidError{c, x509.CANotAuthorizedForThisName, err.Error()}
+		}
+
+		if match {
+			return CertificateInvalidError{c, x509.CANotAuthorizedForThisName, fmt.Sprintf("%s %q is excluded by constraint %q", nameType, name, constraint)}
+		}
+	}
+
+	permittedValue := reflect.ValueOf(permitted)
+
+	*count += permittedValue.Len()
+	if *count > maxConstraintComparisons {
+		return CertificateInvalidError{c, x509.TooManyConstraints, ""}
+	}
+
+	ok := true
+	for i := 0; i < permittedValue.Len(); i++ {
+		constraint := permittedValue.Index(i).Interface()
+
+		var err error
+		if ok, err = match(parsedName, constraint); err != nil {
+			return CertificateInvalidError{c, x509.CANotAuthorizedForThisName, err.Error()}
+		}
+
+		if ok {
+			break
+		}
+	}
+
+	if !ok {
+		return CertificateInvalidError{c, x509.CANotAuthorizedForThisName, fmt.Sprintf("%s %q is not permitted by any constraint", nameType, name)}
+	}
+
+	return nil
+}
+
+// isValid performs validity checks on c given that it is a candidate to append
+// to the chain in currentChain.
+func (c *Certificate) isValid(certType int, currentChain []*Certificate, opts *VerifyOptions) error {
+	if len(c.UnhandledCriticalExtensions) > 0 {
+		return x509.UnhandledCriticalExtension{}
+	}
+
+	if len(currentChain) > 0 {
+		child := currentChain[len(currentChain)-1]
+		if !bytes.Equal(child.RawIssuer, c.RawSubject) {
+			return CertificateInvalidError{c, x509.NameMismatch, ""}
+		}
+	}
+
+	now := opts.CurrentTime
+	if now.IsZero() {
+		now = time.Now()
+	}
+	if now.Before(c.NotBefore) {
+		return CertificateInvalidError{
+			Cert:   c,
+			Reason: x509.Expired,
+			Detail: fmt.Sprintf("current time %s is before %s", now.Format(time.RFC3339), c.NotBefore.Format(time.RFC3339)),
+		}
+	} else if now.After(c.NotAfter) {
+		return CertificateInvalidError{
+			Cert:   c,
+			Reason: x509.Expired,
+			Detail: fmt.Sprintf("current time %s is after %s", now.Format(time.RFC3339), c.NotAfter.Format(time.RFC3339)),
+		}
+	}
+
+	maxConstraintComparisons := opts.MaxConstraintComparisions
+	if maxConstraintComparisons == 0 {
+		maxConstraintComparisons = 250000
+	}
+	comparisonCount := 0
+
+	var leaf *Certificate
+	if certType == intermediateCertificate || certType == rootCertificate {
+		if len(currentChain) == 0 {
+			return errors.New("x509: internal error: empty chain when appending CA cert")
+		}
+		leaf = currentChain[0]
+	}
+
+	checkNameConstraints := (certType == intermediateCertificate || certType == rootCertificate) && c.hasNameConstraints()
+	if checkNameConstraints && leaf.commonNameAsHostname() {
+		// This is the deprecated, legacy case of depending on the commonName as
+		// a hostname. We don't enforce name constraints against the CN, but
+		// VerifyHostname will look for hostnames in there if there are no SANs.
+		// In order to ensure VerifyHostname will not accept an unchecked name,
+		// return an error here.
+		return CertificateInvalidError{c, x509.NameConstraintsWithoutSANs, ""}
+	} else if checkNameConstraints && leaf.hasSANExtension() {
+		err := forEachSAN(leaf.getSANExtension(), func(tag int, data []byte) error {
+			switch tag {
+			case nameTypeEmail:
+				name := string(data)
+				mailbox, ok := parseRFC2821Mailbox(name)
+				if !ok {
+					return fmt.Errorf("x509: cannot parse rfc822Name %q", mailbox)
+				}
+
+				if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "email address", name, mailbox,
+					func(parsedName, constraint interface{}) (bool, error) {
+						return matchEmailConstraint(parsedName.(rfc2821Mailbox), constraint.(string))
+					}, c.PermittedEmailAddresses, c.ExcludedEmailAddresses); err != nil {
+					return err
+				}
+
+			case nameTypeDNS:
+				name := string(data)
+				if _, ok := domainToReverseLabels(name); !ok {
+					return fmt.Errorf("x509: cannot parse dnsName %q", name)
+				}
+
+				if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "DNS name", name, name,
+					func(parsedName, constraint interface{}) (bool, error) {
+						return matchDomainConstraint(parsedName.(string), constraint.(string))
+					}, c.PermittedDNSDomains, c.ExcludedDNSDomains); err != nil {
+					return err
+				}
+
+			case nameTypeURI:
+				name := string(data)
+				uri, err := url.Parse(name)
+				if err != nil {
+					return fmt.Errorf("x509: internal error: URI SAN %q failed to parse", name)
+				}
+
+				if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "URI", name, uri,
+					func(parsedName, constraint interface{}) (bool, error) {
+						return matchURIConstraint(parsedName.(*url.URL), constraint.(string))
+					}, c.PermittedURIDomains, c.ExcludedURIDomains); err != nil {
+					return err
+				}
+
+			case nameTypeIP:
+				ip := net.IP(data)
+				if l := len(ip); l != net.IPv4len && l != net.IPv6len {
+					return fmt.Errorf("x509: internal error: IP SAN %x failed to parse", data)
+				}
+
+				if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "IP address", ip.String(), ip,
+					func(parsedName, constraint interface{}) (bool, error) {
+						return matchIPConstraint(parsedName.(net.IP), constraint.(*net.IPNet))
+					}, c.PermittedIPRanges, c.ExcludedIPRanges); err != nil {
+					return err
+				}
+
+			default:
+				// Unknown SAN types are ignored.
+			}
+
+			return nil
+		})
+
+		if err != nil {
+			return err
+		}
+	}
+
+	// KeyUsage status flags are ignored. From Engineering Security, Peter
+	// Gutmann: A European government CA marked its signing certificates as
+	// being valid for encryption only, but no-one noticed. Another
+	// European CA marked its signature keys as not being valid for
+	// signatures. A different CA marked its own trusted root certificate
+	// as being invalid for certificate signing. Another national CA
+	// distributed a certificate to be used to encrypt data for the
+	// country’s tax authority that was marked as only being usable for
+	// digital signatures but not for encryption. Yet another CA reversed
+	// the order of the bit flags in the keyUsage due to confusion over
+	// encoding endianness, essentially setting a random keyUsage in
+	// certificates that it issued. Another CA created a self-invalidating
+	// certificate by adding a certificate policy statement stipulating
+	// that the certificate had to be used strictly as specified in the
+	// keyUsage, and a keyUsage containing a flag indicating that the RSA
+	// encryption key could only be used for Diffie-Hellman key agreement.
+
+	if certType == intermediateCertificate && (!c.BasicConstraintsValid || !c.IsCA) {
+		return CertificateInvalidError{c, x509.NotAuthorizedToSign, ""}
+	}
+
+	if c.BasicConstraintsValid && c.MaxPathLen >= 0 {
+		numIntermediates := len(currentChain) - 1
+		if numIntermediates > c.MaxPathLen {
+			return CertificateInvalidError{c, x509.TooManyIntermediates, ""}
+		}
+	}
+
+	return nil
+}
+
+// Verify attempts to verify c by building one or more chains from c to a
+// certificate in opts.Roots, using certificates in opts.Intermediates if
+// needed. If successful, it returns one or more chains where the first
+// element of the chain is c and the last element is from opts.Roots.
+//
+// If opts.Roots is nil, the platform verifier might be used, and
+// verification details might differ from what is described below. If system
+// roots are unavailable the returned error will be of type SystemRootsError.
+//
+// Name constraints in the intermediates will be applied to all names claimed
+// in the chain, not just opts.DNSName. Thus it is invalid for a leaf to claim
+// example.com if an intermediate doesn't permit it, even if example.com is not
+// the name being validated. Note that DirectoryName constraints are not
+// supported.
+//
+// Extended Key Usage values are enforced nested down a chain, so an intermediate
+// or root that enumerates EKUs prevents a leaf from asserting an EKU not in that
+// list. (While this is not specified, it is common practice in order to limit
+// the types of certificates a CA can issue.)
+//
+// WARNING: this function doesn't do any revocation checking.
+func (c *Certificate) Verify(opts VerifyOptions) (chains [][]*Certificate, err error) {
+	// Platform-specific verification needs the ASN.1 contents so
+	// this makes the behavior consistent across platforms.
+	if len(c.Raw) == 0 {
+		return nil, errNotParsed
+	}
+	if opts.Intermediates != nil {
+		for _, intermediate := range opts.Intermediates.certs {
+			if len(intermediate.Raw) == 0 {
+				return nil, errNotParsed
+			}
+		}
+	}
+
+	// Use Windows's own verification and chain building.
+	if opts.Roots == nil && runtime.GOOS == "windows" {
+		return c.systemVerify(&opts)
+	}
+
+	if opts.Roots == nil {
+		opts.Roots = systemRootsPool()
+		if opts.Roots == nil {
+			return nil, SystemRootsError{systemRootsErr}
+		}
+	}
+
+	err = c.isValid(leafCertificate, nil, &opts)
+	if err != nil {
+		return
+	}
+
+	if len(opts.DNSName) > 0 {
+		err = c.VerifyHostname(opts.DNSName)
+		if err != nil {
+			return
+		}
+	}
+
+	var candidateChains [][]*Certificate
+	if opts.Roots.contains(c) {
+		candidateChains = append(candidateChains, []*Certificate{c})
+	} else {
+		if candidateChains, err = c.buildChains(nil, []*Certificate{c}, nil, &opts); err != nil {
+			return nil, err
+		}
+	}
+
+	keyUsages := opts.KeyUsages
+	if len(keyUsages) == 0 {
+		keyUsages = []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth}
+	}
+
+	// If any key usage is acceptable then we're done.
+	for _, usage := range keyUsages {
+		if usage == x509.ExtKeyUsageAny {
+			return candidateChains, nil
+		}
+	}
+
+	for _, candidate := range candidateChains {
+		if checkChainForKeyUsage(candidate, keyUsages) {
+			chains = append(chains, candidate)
+		}
+	}
+
+	if len(chains) == 0 {
+		return nil, CertificateInvalidError{c, x509.IncompatibleUsage, ""}
+	}
+
+	return chains, nil
+}
+
+func appendToFreshChain(chain []*Certificate, cert *Certificate) []*Certificate {
+	n := make([]*Certificate, len(chain)+1)
+	copy(n, chain)
+	n[len(chain)] = cert
+	return n
+}
+
+// maxChainSignatureChecks is the maximum number of CheckSignatureFrom calls
+// that an invocation of buildChains will (tranistively) make. Most chains are
+// less than 15 certificates long, so this leaves space for multiple chains and
+// for failed checks due to different intermediates having the same Subject.
+const maxChainSignatureChecks = 100
+
+func (c *Certificate) buildChains(cache map[*Certificate][][]*Certificate, currentChain []*Certificate, sigChecks *int, opts *VerifyOptions) (chains [][]*Certificate, err error) {
+	var (
+		hintErr  error
+		hintCert *Certificate
+	)
+
+	considerCandidate := func(certType int, candidate *Certificate) {
+		for _, cert := range currentChain {
+			if cert.Equal(candidate) {
+				return
+			}
+		}
+
+		if sigChecks == nil {
+			sigChecks = new(int)
+		}
+		*sigChecks++
+		if *sigChecks > maxChainSignatureChecks {
+			err = errors.New("x509: signature check attempts limit reached while verifying certificate chain")
+			return
+		}
+
+		if err := c.CheckSignatureFrom(candidate); err != nil {
+			if hintErr == nil {
+				hintErr = err
+				hintCert = candidate
+			}
+			return
+		}
+
+		err = candidate.isValid(certType, currentChain, opts)
+		if err != nil {
+			return
+		}
+
+		switch certType {
+		case rootCertificate:
+			chains = append(chains, appendToFreshChain(currentChain, candidate))
+		case intermediateCertificate:
+			if cache == nil {
+				cache = make(map[*Certificate][][]*Certificate)
+			}
+			childChains, ok := cache[candidate]
+			if !ok {
+				childChains, err = candidate.buildChains(cache, appendToFreshChain(currentChain, candidate), sigChecks, opts)
+				cache[candidate] = childChains
+			}
+			chains = append(chains, childChains...)
+		}
+	}
+
+	for _, rootNum := range opts.Roots.findPotentialParents(c) {
+		considerCandidate(rootCertificate, opts.Roots.certs[rootNum])
+	}
+	for _, intermediateNum := range opts.Intermediates.findPotentialParents(c) {
+		considerCandidate(intermediateCertificate, opts.Intermediates.certs[intermediateNum])
+	}
+
+	if len(chains) > 0 {
+		err = nil
+	}
+	if len(chains) == 0 && err == nil {
+		err = UnknownAuthorityError{c, hintErr, hintCert}
+	}
+
+	return
+}
+
+// validHostname reports whether host is a valid hostname that can be matched or
+// matched against according to RFC 6125 2.2, with some leniency to accommodate
+// legacy values.
+func validHostname(host string) bool {
+	host = strings.TrimSuffix(host, ".")
+
+	if len(host) == 0 {
+		return false
+	}
+
+	for i, part := range strings.Split(host, ".") {
+		if part == "" {
+			// Empty label.
+			return false
+		}
+		if i == 0 && part == "*" {
+			// Only allow full left-most wildcards, as those are the only ones
+			// we match, and matching literal '*' characters is probably never
+			// the expected behavior.
+			continue
+		}
+		for j, c := range part {
+			if 'a' <= c && c <= 'z' {
+				continue
+			}
+			if '0' <= c && c <= '9' {
+				continue
+			}
+			if 'A' <= c && c <= 'Z' {
+				continue
+			}
+			if c == '-' && j != 0 {
+				continue
+			}
+			if c == '_' || c == ':' {
+				// Not valid characters in hostnames, but commonly
+				// found in deployments outside the WebPKI.
+				continue
+			}
+			return false
+		}
+	}
+
+	return true
+}
+
+// commonNameAsHostname reports whether the Common Name field should be
+// considered the hostname that the certificate is valid for. This is a legacy
+// behavior, disabled if the Subject Alt Name extension is present.
+//
+// It applies the strict validHostname check to the Common Name field, so that
+// certificates without SANs can still be validated against CAs with name
+// constraints if there is no risk the CN would be matched as a hostname.
+// See NameConstraintsWithoutSANs and issue 24151.
+func (c *Certificate) commonNameAsHostname() bool {
+	return !ignoreCN && !c.hasSANExtension() && validHostname(c.Subject.CommonName)
+}
+
+func matchHostnames(pattern, host string) bool {
+	host = strings.TrimSuffix(host, ".")
+	pattern = strings.TrimSuffix(pattern, ".")
+
+	if len(pattern) == 0 || len(host) == 0 {
+		return false
+	}
+
+	patternParts := strings.Split(pattern, ".")
+	hostParts := strings.Split(host, ".")
+
+	if len(patternParts) != len(hostParts) {
+		return false
+	}
+
+	for i, patternPart := range patternParts {
+		if i == 0 && patternPart == "*" {
+			continue
+		}
+		if patternPart != hostParts[i] {
+			return false
+		}
+	}
+
+	return true
+}
+
+// toLowerCaseASCII returns a lower-case version of in. See RFC 6125 6.4.1. We use
+// an explicitly ASCII function to avoid any sharp corners resulting from
+// performing Unicode operations on DNS labels.
+func toLowerCaseASCII(in string) string {
+	// If the string is already lower-case then there's nothing to do.
+	isAlreadyLowerCase := true
+	for _, c := range in {
+		if c == utf8.RuneError {
+			// If we get a UTF-8 error then there might be
+			// upper-case ASCII bytes in the invalid sequence.
+			isAlreadyLowerCase = false
+			break
+		}
+		if 'A' <= c && c <= 'Z' {
+			isAlreadyLowerCase = false
+			break
+		}
+	}
+
+	if isAlreadyLowerCase {
+		return in
+	}
+
+	out := []byte(in)
+	for i, c := range out {
+		if 'A' <= c && c <= 'Z' {
+			out[i] += 'a' - 'A'
+		}
+	}
+	return string(out)
+}
+
+// VerifyHostname returns nil if c is a valid certificate for the named host.
+// Otherwise it returns an error describing the mismatch.
+func (c *Certificate) VerifyHostname(h string) error {
+	// IP addresses may be written in [ ].
+	candidateIP := h
+	if len(h) >= 3 && h[0] == '[' && h[len(h)-1] == ']' {
+		candidateIP = h[1 : len(h)-1]
+	}
+	if ip := net.ParseIP(candidateIP); ip != nil {
+		// We only match IP addresses against IP SANs.
+		// See RFC 6125, Appendix B.2.
+		for _, candidate := range c.IPAddresses {
+			if ip.Equal(candidate) {
+				return nil
+			}
+		}
+		return x509.HostnameError{&c.Certificate, candidateIP}
+	}
+
+	lowered := toLowerCaseASCII(h)
+
+	if c.commonNameAsHostname() {
+		if matchHostnames(toLowerCaseASCII(c.Subject.CommonName), lowered) {
+			return nil
+		}
+	} else {
+		for _, match := range c.DNSNames {
+			if matchHostnames(toLowerCaseASCII(match), lowered) {
+				return nil
+			}
+		}
+	}
+
+	return x509.HostnameError{&c.Certificate, h}
+}
+
+func checkChainForKeyUsage(chain []*Certificate, keyUsages []x509.ExtKeyUsage) bool {
+	usages := make([]x509.ExtKeyUsage, len(keyUsages))
+	copy(usages, keyUsages)
+
+	if len(chain) == 0 {
+		return false
+	}
+
+	usagesRemaining := len(usages)
+
+	// We walk down the list and cross out any usages that aren't supported
+	// by each certificate. If we cross out all the usages, then the chain
+	// is unacceptable.
+
+NextCert:
+	for i := len(chain) - 1; i >= 0; i-- {
+		cert := chain[i]
+		if len(cert.ExtKeyUsage) == 0 && len(cert.UnknownExtKeyUsage) == 0 {
+			// The certificate doesn't have any extended key usage specified.
+			continue
+		}
+
+		for _, usage := range cert.ExtKeyUsage {
+			if usage == x509.ExtKeyUsageAny {
+				// The certificate is explicitly good for any usage.
+				continue NextCert
+			}
+		}
+
+		const invalidUsage x509.ExtKeyUsage = -1
+
+	NextRequestedUsage:
+		for i, requestedUsage := range usages {
+			if requestedUsage == invalidUsage {
+				continue
+			}
+
+			for _, usage := range cert.ExtKeyUsage {
+				if requestedUsage == usage {
+					continue NextRequestedUsage
+				} else if requestedUsage == x509.ExtKeyUsageServerAuth &&
+					(usage == x509.ExtKeyUsageNetscapeServerGatedCrypto ||
+						usage == x509.ExtKeyUsageMicrosoftServerGatedCrypto) {
+					// In order to support COMODO
+					// certificate chains, we have to
+					// accept Netscape or Microsoft SGC
+					// usages as equal to ServerAuth.
+					continue NextRequestedUsage
+				}
+			}
+
+			usages[i] = invalidUsage
+			usagesRemaining--
+			if usagesRemaining == 0 {
+				return false
+			}
+		}
+	}
+
+	return true
+}
+
+func matchEmailConstraint(mailbox rfc2821Mailbox, constraint string) (bool, error) {
+	// If the constraint contains an @, then it specifies an exact mailbox
+	// name.
+	if strings.Contains(constraint, "@") {
+		constraintMailbox, ok := parseRFC2821Mailbox(constraint)
+		if !ok {
+			return false, fmt.Errorf("x509: internal error: cannot parse constraint %q", constraint)
+		}
+		return mailbox.local == constraintMailbox.local && strings.EqualFold(mailbox.domain, constraintMailbox.domain), nil
+	}
+
+	// Otherwise the constraint is like a DNS constraint of the domain part
+	// of the mailbox.
+	return matchDomainConstraint(mailbox.domain, constraint)
+}
+
+func matchURIConstraint(uri *url.URL, constraint string) (bool, error) {
+	// From RFC 5280, Section 4.2.1.10:
+	// “a uniformResourceIdentifier that does not include an authority
+	// component with a host name specified as a fully qualified domain
+	// name (e.g., if the URI either does not include an authority
+	// component or includes an authority component in which the host name
+	// is specified as an IP address), then the application MUST reject the
+	// certificate.”
+
+	host := uri.Host
+	if len(host) == 0 {
+		return false, fmt.Errorf("URI with empty host (%q) cannot be matched against constraints", uri.String())
+	}
+
+	if strings.Contains(host, ":") && !strings.HasSuffix(host, "]") {
+		var err error
+		host, _, err = net.SplitHostPort(uri.Host)
+		if err != nil {
+			return false, err
+		}
+	}
+
+	if strings.HasPrefix(host, "[") && strings.HasSuffix(host, "]") ||
+		net.ParseIP(host) != nil {
+		return false, fmt.Errorf("URI with IP (%q) cannot be matched against constraints", uri.String())
+	}
+
+	return matchDomainConstraint(host, constraint)
+}
+
+func matchIPConstraint(ip net.IP, constraint *net.IPNet) (bool, error) {
+	if len(ip) != len(constraint.IP) {
+		return false, nil
+	}
+
+	for i := range ip {
+		if mask := constraint.Mask[i]; ip[i]&mask != constraint.IP[i]&mask {
+			return false, nil
+		}
+	}
+
+	return true, nil
+}
+
+func matchDomainConstraint(domain, constraint string) (bool, error) {
+	// The meaning of zero length constraints is not specified, but this
+	// code follows NSS and accepts them as matching everything.
+	if len(constraint) == 0 {
+		return true, nil
+	}
+
+	domainLabels, ok := domainToReverseLabels(domain)
+	if !ok {
+		return false, fmt.Errorf("x509: internal error: cannot parse domain %q", domain)
+	}
+
+	// RFC 5280 says that a leading period in a domain name means that at
+	// least one label must be prepended, but only for URI and email
+	// constraints, not DNS constraints. The code also supports that
+	// behaviour for DNS constraints.
+
+	mustHaveSubdomains := false
+	if constraint[0] == '.' {
+		mustHaveSubdomains = true
+		constraint = constraint[1:]
+	}
+
+	constraintLabels, ok := domainToReverseLabels(constraint)
+	if !ok {
+		return false, fmt.Errorf("x509: internal error: cannot parse domain %q", constraint)
+	}
+
+	if len(domainLabels) < len(constraintLabels) ||
+		(mustHaveSubdomains && len(domainLabels) == len(constraintLabels)) {
+		return false, nil
+	}
+
+	for i, constraintLabel := range constraintLabels {
+		if !strings.EqualFold(constraintLabel, domainLabels[i]) {
+			return false, nil
+		}
+	}
+
+	return true, nil
+}
diff --git a/smx509/x509.go b/smx509/x509.go
index 93febaf..6008755 100644
--- a/smx509/x509.go
+++ b/smx509/x509.go
@@ -1,9 +1,13 @@
 package smx509
 
 import (
+	"bytes"
 	"crypto"
+	"crypto/dsa"
 	"crypto/ecdsa"
+	"crypto/ed25519"
 	"crypto/elliptic"
+	"crypto/rsa"
 	"crypto/x509"
 	"crypto/x509/pkix"
 	"encoding/asn1"
@@ -15,6 +19,11 @@ import (
 	"net/url"
 	"strconv"
 	"strings"
+	"time"
+	"unicode/utf8"
+
+	"golang.org/x/crypto/cryptobyte"
+	cryptobyte_asn1 "golang.org/x/crypto/cryptobyte/asn1"
 
 	"github.com/emmansun/gmsm/sm2"
 )
@@ -32,12 +41,47 @@ type publicKeyInfo struct {
 	PublicKey asn1.BitString
 }
 
+// These structures reflect the ASN.1 structure of X.509 certificates.:
+type validity struct {
+	NotBefore, NotAfter time.Time
+}
+
+type certificate struct {
+	Raw                asn1.RawContent
+	TBSCertificate     tbsCertificate
+	SignatureAlgorithm pkix.AlgorithmIdentifier
+	SignatureValue     asn1.BitString
+}
+
+type tbsCertificate struct {
+	Raw                asn1.RawContent
+	Version            int `asn1:"optional,explicit,default:0,tag:0"`
+	SerialNumber       *big.Int
+	SignatureAlgorithm pkix.AlgorithmIdentifier
+	Issuer             asn1.RawValue
+	Validity           validity
+	Subject            asn1.RawValue
+	PublicKey          publicKeyInfo
+	UniqueId           asn1.BitString   `asn1:"optional,tag:1"`
+	SubjectUniqueId    asn1.BitString   `asn1:"optional,tag:2"`
+	Extensions         []pkix.Extension `asn1:"optional,explicit,tag:3"`
+}
+
+// RFC 5280,  4.2.1.1
+type authKeyId struct {
+	Id []byte `asn1:"optional,tag:0"`
+}
+
 // pkcs1PublicKey reflects the ASN.1 structure of a PKCS#1 public key.
 type pkcs1PublicKey struct {
 	N *big.Int
 	E int
 }
 
+type dsaAlgorithmParameters struct {
+	P, Q, G *big.Int
+}
+
 type ecdsaSignature struct {
 	R, S *big.Int
 }
@@ -50,9 +94,34 @@ var (
 	oidNamedCurveP521    = asn1.ObjectIdentifier{1, 3, 132, 0, 35}
 	oidNamedCurveP256SM2 = asn1.ObjectIdentifier{1, 2, 156, 10197, 1, 301}
 
-	oidSignatureSM2WithSM3    = asn1.ObjectIdentifier{1, 2, 156, 10197, 1, 501}
-	oidSignatureSM2WithSHA1   = asn1.ObjectIdentifier{1, 2, 156, 10197, 1, 502}
-	oidSignatureSM2WithSHA256 = asn1.ObjectIdentifier{1, 2, 156, 10197, 1, 503}
+	oidSignatureMD2WithRSA      = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 2}
+	oidSignatureMD5WithRSA      = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 4}
+	oidSignatureSHA1WithRSA     = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 5}
+	oidSignatureSHA256WithRSA   = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 11}
+	oidSignatureSHA384WithRSA   = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 12}
+	oidSignatureSHA512WithRSA   = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 13}
+	oidSignatureRSAPSS          = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 10}
+	oidSignatureDSAWithSHA1     = asn1.ObjectIdentifier{1, 2, 840, 10040, 4, 3}
+	oidSignatureDSAWithSHA256   = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 3, 4, 3, 2}
+	oidSignatureECDSAWithSHA1   = asn1.ObjectIdentifier{1, 2, 840, 10045, 4, 1}
+	oidSignatureECDSAWithSHA256 = asn1.ObjectIdentifier{1, 2, 840, 10045, 4, 3, 2}
+	oidSignatureECDSAWithSHA384 = asn1.ObjectIdentifier{1, 2, 840, 10045, 4, 3, 3}
+	oidSignatureECDSAWithSHA512 = asn1.ObjectIdentifier{1, 2, 840, 10045, 4, 3, 4}
+	oidSignatureEd25519         = asn1.ObjectIdentifier{1, 3, 101, 112}
+	oidSignatureSM2WithSM3      = asn1.ObjectIdentifier{1, 2, 156, 10197, 1, 501}
+	oidSignatureSM2WithSHA1     = asn1.ObjectIdentifier{1, 2, 156, 10197, 1, 502}
+	oidSignatureSM2WithSHA256   = asn1.ObjectIdentifier{1, 2, 156, 10197, 1, 503}
+
+	oidSHA256 = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 3, 4, 2, 1}
+	oidSHA384 = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 3, 4, 2, 2}
+	oidSHA512 = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 3, 4, 2, 3}
+
+	oidMGF1 = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 8}
+
+	// oidISOSignatureSHA1WithRSA means the same as oidSignatureSHA1WithRSA
+	// but it's specified by ISO. Microsoft's makecert.exe has been known
+	// to produce certificates with this OID.
+	oidISOSignatureSHA1WithRSA = asn1.ObjectIdentifier{1, 3, 14, 3, 2, 29}
 )
 
 func oidFromNamedCurve(curve elliptic.Curve) (asn1.ObjectIdentifier, bool) {
@@ -88,6 +157,89 @@ func namedCurveFromOID(oid asn1.ObjectIdentifier) elliptic.Curve {
 	return nil
 }
 
+var signatureAlgorithmDetails = []struct {
+	algo       x509.SignatureAlgorithm
+	name       string
+	oid        asn1.ObjectIdentifier
+	pubKeyAlgo x509.PublicKeyAlgorithm
+	hash       crypto.Hash
+}{
+	{x509.MD2WithRSA, "MD2-RSA", oidSignatureMD2WithRSA, x509.RSA, crypto.Hash(0) /* no value for MD2 */},
+	{x509.MD5WithRSA, "MD5-RSA", oidSignatureMD5WithRSA, x509.RSA, crypto.MD5},
+	{x509.SHA1WithRSA, "SHA1-RSA", oidSignatureSHA1WithRSA, x509.RSA, crypto.SHA1},
+	{x509.SHA1WithRSA, "SHA1-RSA", oidISOSignatureSHA1WithRSA, x509.RSA, crypto.SHA1},
+	{x509.SHA256WithRSA, "SHA256-RSA", oidSignatureSHA256WithRSA, x509.RSA, crypto.SHA256},
+	{x509.SHA384WithRSA, "SHA384-RSA", oidSignatureSHA384WithRSA, x509.RSA, crypto.SHA384},
+	{x509.SHA512WithRSA, "SHA512-RSA", oidSignatureSHA512WithRSA, x509.RSA, crypto.SHA512},
+	{x509.SHA256WithRSAPSS, "SHA256-RSAPSS", oidSignatureRSAPSS, x509.RSA, crypto.SHA256},
+	{x509.SHA384WithRSAPSS, "SHA384-RSAPSS", oidSignatureRSAPSS, x509.RSA, crypto.SHA384},
+	{x509.SHA512WithRSAPSS, "SHA512-RSAPSS", oidSignatureRSAPSS, x509.RSA, crypto.SHA512},
+	{x509.DSAWithSHA1, "DSA-SHA1", oidSignatureDSAWithSHA1, x509.DSA, crypto.SHA1},
+	{x509.DSAWithSHA256, "DSA-SHA256", oidSignatureDSAWithSHA256, x509.DSA, crypto.SHA256},
+	{x509.ECDSAWithSHA1, "ECDSA-SHA1", oidSignatureECDSAWithSHA1, x509.ECDSA, crypto.SHA1},
+	{x509.ECDSAWithSHA256, "ECDSA-SHA256", oidSignatureECDSAWithSHA256, x509.ECDSA, crypto.SHA256},
+	{x509.ECDSAWithSHA384, "ECDSA-SHA384", oidSignatureECDSAWithSHA384, x509.ECDSA, crypto.SHA384},
+	{x509.ECDSAWithSHA512, "ECDSA-SHA512", oidSignatureECDSAWithSHA512, x509.ECDSA, crypto.SHA512},
+	{x509.PureEd25519, "Ed25519", oidSignatureEd25519, x509.Ed25519, crypto.Hash(0) /* no pre-hashing */},
+}
+
+// pssParameters reflects the parameters in an AlgorithmIdentifier that
+// specifies RSA PSS. See RFC 3447, Appendix A.2.3.
+type pssParameters struct {
+	// The following three fields are not marked as
+	// optional because the default values specify SHA-1,
+	// which is no longer suitable for use in signatures.
+	Hash         pkix.AlgorithmIdentifier `asn1:"explicit,tag:0"`
+	MGF          pkix.AlgorithmIdentifier `asn1:"explicit,tag:1"`
+	SaltLength   int                      `asn1:"explicit,tag:2"`
+	TrailerField int                      `asn1:"optional,explicit,tag:3,default:1"`
+}
+
+// rsaPSSParameters returns an asn1.RawValue suitable for use as the Parameters
+// in an AlgorithmIdentifier that specifies RSA PSS.
+func rsaPSSParameters(hashFunc crypto.Hash) asn1.RawValue {
+	var hashOID asn1.ObjectIdentifier
+
+	switch hashFunc {
+	case crypto.SHA256:
+		hashOID = oidSHA256
+	case crypto.SHA384:
+		hashOID = oidSHA384
+	case crypto.SHA512:
+		hashOID = oidSHA512
+	}
+
+	params := pssParameters{
+		Hash: pkix.AlgorithmIdentifier{
+			Algorithm:  hashOID,
+			Parameters: asn1.NullRawValue,
+		},
+		MGF: pkix.AlgorithmIdentifier{
+			Algorithm: oidMGF1,
+		},
+		SaltLength:   hashFunc.Size(),
+		TrailerField: 1,
+	}
+
+	mgf1Params := pkix.AlgorithmIdentifier{
+		Algorithm:  hashOID,
+		Parameters: asn1.NullRawValue,
+	}
+
+	var err error
+	params.MGF.Parameters.FullBytes, err = asn1.Marshal(mgf1Params)
+	if err != nil {
+		panic(err)
+	}
+
+	serialized, err := asn1.Marshal(params)
+	if err != nil {
+		panic(err)
+	}
+
+	return asn1.RawValue{FullBytes: serialized}
+}
+
 // ParsePKIXPublicKey parses a public key in PKIX, ASN.1 DER form.
 //
 // It returns a *rsa.PublicKey, *dsa.PublicKey, *ecdsa.PublicKey, or
@@ -142,13 +294,11 @@ func ParsePKIXPublicKey(derBytes []byte) (interface{}, error) {
 //
 // This kind of key is commonly encoded in PEM blocks of type "PUBLIC KEY".
 func MarshalPKIXPublicKey(pub interface{}) ([]byte, error) {
-	ecdPub, ok := pub.(*ecdsa.PublicKey)
-	if !ok || ecdPub.Curve != sm2.P256() {
-		return x509.MarshalPKIXPublicKey(pub)
-	}
+	var publicKeyBytes []byte
+	var publicKeyAlgorithm pkix.AlgorithmIdentifier
+	var err error
 
-	publicKeyBytes, publicKeyAlgorithm, err := marshalPublicKey(ecdPub)
-	if err != nil {
+	if publicKeyBytes, publicKeyAlgorithm, err = marshalPublicKey(pub); err != nil {
 		return nil, err
 	}
 
@@ -160,15 +310,45 @@ func MarshalPKIXPublicKey(pub interface{}) ([]byte, error) {
 		},
 	}
 
-	return asn1.Marshal(pkix)
+	ret, _ := asn1.Marshal(pkix)
+	return ret, nil
 }
 
-func marshalPublicKey(pub *ecdsa.PublicKey) (publicKeyBytes []byte, publicKeyAlgorithm pkix.AlgorithmIdentifier, err error) {
-	publicKeyAlgorithm = pkix.AlgorithmIdentifier{Algorithm: oidPublicKeyECDSA}
-	publicKeyBytes = elliptic.Marshal(pub.Curve, pub.X, pub.Y)
-	paramBytes, err := asn1.Marshal(oidNamedCurveP256SM2)
-	publicKeyAlgorithm.Parameters.FullBytes = paramBytes
-	return
+func marshalPublicKey(pub interface{}) (publicKeyBytes []byte, publicKeyAlgorithm pkix.AlgorithmIdentifier, err error) {
+	switch pub := pub.(type) {
+	case *rsa.PublicKey:
+		publicKeyBytes, err = asn1.Marshal(pkcs1PublicKey{
+			N: pub.N,
+			E: pub.E,
+		})
+		if err != nil {
+			return nil, pkix.AlgorithmIdentifier{}, err
+		}
+		publicKeyAlgorithm.Algorithm = oidPublicKeyRSA
+		// This is a NULL parameters value which is required by
+		// RFC 3279, Section 2.3.1.
+		publicKeyAlgorithm.Parameters = asn1.NullRawValue
+	case *ecdsa.PublicKey:
+		publicKeyBytes = elliptic.Marshal(pub.Curve, pub.X, pub.Y)
+		oid, ok := oidFromNamedCurve(pub.Curve)
+		if !ok {
+			return nil, pkix.AlgorithmIdentifier{}, errors.New("x509: unsupported elliptic curve")
+		}
+		publicKeyAlgorithm.Algorithm = oidPublicKeyECDSA
+		var paramBytes []byte
+		paramBytes, err = asn1.Marshal(oid)
+		if err != nil {
+			return
+		}
+		publicKeyAlgorithm.Parameters.FullBytes = paramBytes
+	case ed25519.PublicKey:
+		publicKeyBytes = pub
+		publicKeyAlgorithm.Algorithm = oidPublicKeyEd25519
+	default:
+		return nil, pkix.AlgorithmIdentifier{}, fmt.Errorf("x509: unsupported public key type: %T", pub)
+	}
+
+	return publicKeyBytes, publicKeyAlgorithm, nil
 }
 
 // CreateCertificateRequest creates a new certificate request based on a
@@ -197,7 +377,11 @@ func CreateCertificateRequest(rand io.Reader, template *x509.CertificateRequest,
 	}
 	privKey, ok := key.(*sm2.PrivateKey)
 	if !ok {
-		return x509.CreateCertificateRequest(rand, template, priv)
+		ecKey, ok := key.(*ecdsa.PrivateKey)
+		if !ok || ecKey.Curve != sm2.P256() {
+			return x509.CreateCertificateRequest(rand, template, priv)
+		}
+		privKey, _ = new(sm2.PrivateKey).FromECPrivateKey(ecKey)
 	}
 	var sigAlgo = pkix.AlgorithmIdentifier{}
 	sigAlgo.Algorithm = oidSignatureSM2WithSM3
@@ -448,7 +632,7 @@ func marshalSANs(dnsNames, emailAddresses []string, ipAddresses []net.IP, uris [
 
 // ParseCertificateRequest parses a single certificate request from the
 // given ASN.1 DER data.
-func ParseCertificateRequest(asn1Data []byte) (*x509.CertificateRequest, error) {
+func ParseCertificateRequest(asn1Data []byte) (*CertificateRequest, error) {
 	var csr certificateRequest
 
 	rest, err := asn1.Unmarshal(asn1Data, &csr)
@@ -458,16 +642,20 @@ func ParseCertificateRequest(asn1Data []byte) (*x509.CertificateRequest, error)
 		return nil, asn1.SyntaxError{Msg: "trailing data"}
 	}
 	if !csr.SignatureAlgorithm.Algorithm.Equal(oidSignatureSM2WithSM3) {
-		return x509.ParseCertificateRequest(asn1Data)
+		csrR, err := x509.ParseCertificateRequest(asn1Data)
+		if err != nil {
+			return nil, err
+		}
+		return &CertificateRequest{*csrR}, nil
 	}
 	return parseCertificateRequest(&csr)
 }
 
-func parseCertificateRequest(in *certificateRequest) (*x509.CertificateRequest, error) {
+func parseCertificateRequest(in *certificateRequest) (*CertificateRequest, error) {
 	if !oidSignatureSM2WithSM3.Equal(in.SignatureAlgorithm.Algorithm) {
 		return nil, errors.New("unsupport signature algorithm")
 	}
-	out := &x509.CertificateRequest{
+	out := &CertificateRequest{x509.CertificateRequest{
 		Raw:                      in.Raw,
 		RawTBSCertificateRequest: in.TBSCSR.Raw,
 		RawSubjectPublicKeyInfo:  in.TBSCSR.PublicKey.Raw,
@@ -479,10 +667,11 @@ func parseCertificateRequest(in *certificateRequest) (*x509.CertificateRequest,
 
 		Version:    in.TBSCSR.Version,
 		Attributes: parseRawAttributes(in.TBSCSR.RawAttributes),
+	},
 	}
 
 	var err error
-	out.PublicKey, err = parsePublicKey(&in.TBSCSR.PublicKey)
+	out.PublicKey, err = parsePublicKey(out.PublicKeyAlgorithm, &in.TBSCSR.PublicKey)
 	if err != nil {
 		return nil, err
 	}
@@ -512,31 +701,106 @@ func parseCertificateRequest(in *certificateRequest) (*x509.CertificateRequest,
 	return out, nil
 }
 
-func parsePublicKey(keyData *publicKeyInfo) (interface{}, error) {
+func parsePublicKey(algo x509.PublicKeyAlgorithm, keyData *publicKeyInfo) (interface{}, error) {
 	asn1Data := keyData.PublicKey.RightAlign()
-	paramsData := keyData.Algorithm.Parameters.FullBytes
-	namedCurveOID := new(asn1.ObjectIdentifier)
-	rest, err := asn1.Unmarshal(paramsData, namedCurveOID)
-	if err != nil {
-		return nil, errors.New("x509: failed to parse ECDSA parameters as named curve")
+	switch algo {
+	case x509.RSA:
+		// RSA public keys must have a NULL in the parameters.
+		// See RFC 3279, Section 2.3.1.
+		if !bytes.Equal(keyData.Algorithm.Parameters.FullBytes, asn1.NullBytes) {
+			return nil, errors.New("x509: RSA key missing NULL parameters")
+		}
+
+		p := new(pkcs1PublicKey)
+		rest, err := asn1.Unmarshal(asn1Data, p)
+		if err != nil {
+			return nil, err
+		}
+		if len(rest) != 0 {
+			return nil, errors.New("x509: trailing data after RSA public key")
+		}
+
+		if p.N.Sign() <= 0 {
+			return nil, errors.New("x509: RSA modulus is not a positive number")
+		}
+		if p.E <= 0 {
+			return nil, errors.New("x509: RSA public exponent is not a positive number")
+		}
+
+		pub := &rsa.PublicKey{
+			E: p.E,
+			N: p.N,
+		}
+		return pub, nil
+	case x509.DSA:
+		var p *big.Int
+		rest, err := asn1.Unmarshal(asn1Data, &p)
+		if err != nil {
+			return nil, err
+		}
+		if len(rest) != 0 {
+			return nil, errors.New("x509: trailing data after DSA public key")
+		}
+		paramsData := keyData.Algorithm.Parameters.FullBytes
+		params := new(dsaAlgorithmParameters)
+		rest, err = asn1.Unmarshal(paramsData, params)
+		if err != nil {
+			return nil, err
+		}
+		if len(rest) != 0 {
+			return nil, errors.New("x509: trailing data after DSA parameters")
+		}
+		if p.Sign() <= 0 || params.P.Sign() <= 0 || params.Q.Sign() <= 0 || params.G.Sign() <= 0 {
+			return nil, errors.New("x509: zero or negative DSA parameter")
+		}
+		pub := &dsa.PublicKey{
+			Parameters: dsa.Parameters{
+				P: params.P,
+				Q: params.Q,
+				G: params.G,
+			},
+			Y: p,
+		}
+		return pub, nil
+	case x509.ECDSA:
+		paramsData := keyData.Algorithm.Parameters.FullBytes
+		namedCurveOID := new(asn1.ObjectIdentifier)
+		rest, err := asn1.Unmarshal(paramsData, namedCurveOID)
+		if err != nil {
+			return nil, errors.New("x509: failed to parse ECDSA parameters as named curve")
+		}
+		if len(rest) != 0 {
+			return nil, errors.New("x509: trailing data after ECDSA parameters")
+		}
+		namedCurve := namedCurveFromOID(*namedCurveOID)
+		if namedCurve == nil {
+			return nil, errors.New("x509: unsupported elliptic curve")
+		}
+		x, y := elliptic.Unmarshal(namedCurve, asn1Data)
+		if x == nil {
+			return nil, errors.New("x509: failed to unmarshal elliptic curve point")
+		}
+		pub := &ecdsa.PublicKey{
+			Curve: namedCurve,
+			X:     x,
+			Y:     y,
+		}
+		return pub, nil
+	case x509.Ed25519:
+		// RFC 8410, Section 3
+		// > For all of the OIDs, the parameters MUST be absent.
+		if len(keyData.Algorithm.Parameters.FullBytes) != 0 {
+			return nil, errors.New("x509: Ed25519 key encoded with illegal parameters")
+		}
+		if len(asn1Data) != ed25519.PublicKeySize {
+			return nil, errors.New("x509: wrong Ed25519 public key size")
+		}
+		pub := make([]byte, ed25519.PublicKeySize)
+		copy(pub, asn1Data)
+		return ed25519.PublicKey(pub), nil
+	default:
+		return nil, nil
 	}
-	if len(rest) != 0 {
-		return nil, errors.New("x509: trailing data after ECDSA parameters")
-	}
-	namedCurve := namedCurveFromOID(*namedCurveOID)
-	if namedCurve == nil {
-		return nil, errors.New("x509: unsupported elliptic curve")
-	}
-	x, y := elliptic.Unmarshal(namedCurve, asn1Data)
-	if x == nil {
-		return nil, errors.New("x509: failed to unmarshal elliptic curve point")
-	}
-	pub := &ecdsa.PublicKey{
-		Curve: namedCurve,
-		X:     x,
-		Y:     y,
-	}
-	return pub, nil
 }
 
 // parseRawAttributes Unmarshals RawAttributes into AttributeTypeAndValueSETs.
@@ -712,14 +976,22 @@ func parseSANExtension(value []byte) (dnsNames, emailAddresses []string, ipAddre
 // id-ecPublicKey OBJECT IDENTIFIER ::= {
 //       iso(1) member-body(2) us(840) ansi-X9-62(10045) keyType(2) 1 }
 var (
-	oidPublicKeyRSA   = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 1}
-	oidPublicKeyDSA   = asn1.ObjectIdentifier{1, 2, 840, 10040, 4, 1}
-	oidPublicKeyECDSA = asn1.ObjectIdentifier{1, 2, 840, 10045, 2, 1}
+	oidPublicKeyRSA     = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 1}
+	oidPublicKeyDSA     = asn1.ObjectIdentifier{1, 2, 840, 10040, 4, 1}
+	oidPublicKeyECDSA   = asn1.ObjectIdentifier{1, 2, 840, 10045, 2, 1}
+	oidPublicKeyEd25519 = asn1.ObjectIdentifier{1, 3, 101, 112}
 )
 
 func getPublicKeyAlgorithmFromOID(oid asn1.ObjectIdentifier) x509.PublicKeyAlgorithm {
-	if oid.Equal(oidPublicKeyECDSA) {
+	switch {
+	case oid.Equal(oidPublicKeyRSA):
+		return x509.RSA
+	case oid.Equal(oidPublicKeyDSA):
+		return x509.DSA
+	case oid.Equal(oidPublicKeyECDSA):
 		return x509.ECDSA
+	case oid.Equal(oidPublicKeyEd25519):
+		return x509.Ed25519
 	}
 	return x509.UnknownPublicKeyAlgorithm
 }
@@ -735,6 +1007,16 @@ func CheckSignature(c *x509.CertificateRequest) error {
 	return c.CheckSignature()
 }
 
+// CertificateRequest represents a PKCS #10, certificate signature request.
+type CertificateRequest struct {
+	x509.CertificateRequest
+}
+
+// CheckSignature reports whether the signature on c is valid.
+func (c *CertificateRequest) CheckSignature() error {
+	return CheckSignature(&c.CertificateRequest)
+}
+
 // CheckSignature verifies that signature is a valid signature over signed from
 // a crypto.PublicKey.
 func checkSignature(c *x509.CertificateRequest, publicKey *ecdsa.PublicKey) (err error) {
@@ -753,3 +1035,1311 @@ func checkSignature(c *x509.CertificateRequest, publicKey *ecdsa.PublicKey) (err
 	}
 	return
 }
+
+func reverseBitsInAByte(in byte) byte {
+	b1 := in>>4 | in<<4
+	b2 := b1>>2&0x33 | b1<<2&0xcc
+	b3 := b2>>1&0x55 | b2<<1&0xaa
+	return b3
+}
+
+// asn1BitLength returns the bit-length of bitString by considering the
+// most-significant bit in a byte to be the "first" bit. This convention
+// matches ASN.1, but differs from almost everything else.
+func asn1BitLength(bitString []byte) int {
+	bitLen := len(bitString) * 8
+
+	for i := range bitString {
+		b := bitString[len(bitString)-i-1]
+
+		for bit := uint(0); bit < 8; bit++ {
+			if (b>>bit)&1 == 1 {
+				return bitLen
+			}
+			bitLen--
+		}
+	}
+
+	return 0
+}
+
+// RFC 5280, 4.2.1.12  Extended Key Usage
+//
+// anyExtendedKeyUsage OBJECT IDENTIFIER ::= { id-ce-extKeyUsage 0 }
+//
+// id-kp OBJECT IDENTIFIER ::= { id-pkix 3 }
+//
+// id-kp-serverAuth             OBJECT IDENTIFIER ::= { id-kp 1 }
+// id-kp-clientAuth             OBJECT IDENTIFIER ::= { id-kp 2 }
+// id-kp-codeSigning            OBJECT IDENTIFIER ::= { id-kp 3 }
+// id-kp-emailProtection        OBJECT IDENTIFIER ::= { id-kp 4 }
+// id-kp-timeStamping           OBJECT IDENTIFIER ::= { id-kp 8 }
+// id-kp-OCSPSigning            OBJECT IDENTIFIER ::= { id-kp 9 }
+var (
+	oidExtKeyUsageAny                            = asn1.ObjectIdentifier{2, 5, 29, 37, 0}
+	oidExtKeyUsageServerAuth                     = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 1}
+	oidExtKeyUsageClientAuth                     = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 2}
+	oidExtKeyUsageCodeSigning                    = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 3}
+	oidExtKeyUsageEmailProtection                = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 4}
+	oidExtKeyUsageIPSECEndSystem                 = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 5}
+	oidExtKeyUsageIPSECTunnel                    = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 6}
+	oidExtKeyUsageIPSECUser                      = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 7}
+	oidExtKeyUsageTimeStamping                   = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 8}
+	oidExtKeyUsageOCSPSigning                    = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 9}
+	oidExtKeyUsageMicrosoftServerGatedCrypto     = asn1.ObjectIdentifier{1, 3, 6, 1, 4, 1, 311, 10, 3, 3}
+	oidExtKeyUsageNetscapeServerGatedCrypto      = asn1.ObjectIdentifier{2, 16, 840, 1, 113730, 4, 1}
+	oidExtKeyUsageMicrosoftCommercialCodeSigning = asn1.ObjectIdentifier{1, 3, 6, 1, 4, 1, 311, 2, 1, 22}
+	oidExtKeyUsageMicrosoftKernelCodeSigning     = asn1.ObjectIdentifier{1, 3, 6, 1, 4, 1, 311, 61, 1, 1}
+)
+
+// extKeyUsageOIDs contains the mapping between an ExtKeyUsage and its OID.
+var extKeyUsageOIDs = []struct {
+	extKeyUsage x509.ExtKeyUsage
+	oid         asn1.ObjectIdentifier
+}{
+	{x509.ExtKeyUsageAny, oidExtKeyUsageAny},
+	{x509.ExtKeyUsageServerAuth, oidExtKeyUsageServerAuth},
+	{x509.ExtKeyUsageClientAuth, oidExtKeyUsageClientAuth},
+	{x509.ExtKeyUsageCodeSigning, oidExtKeyUsageCodeSigning},
+	{x509.ExtKeyUsageEmailProtection, oidExtKeyUsageEmailProtection},
+	{x509.ExtKeyUsageIPSECEndSystem, oidExtKeyUsageIPSECEndSystem},
+	{x509.ExtKeyUsageIPSECTunnel, oidExtKeyUsageIPSECTunnel},
+	{x509.ExtKeyUsageIPSECUser, oidExtKeyUsageIPSECUser},
+	{x509.ExtKeyUsageTimeStamping, oidExtKeyUsageTimeStamping},
+	{x509.ExtKeyUsageOCSPSigning, oidExtKeyUsageOCSPSigning},
+	{x509.ExtKeyUsageMicrosoftServerGatedCrypto, oidExtKeyUsageMicrosoftServerGatedCrypto},
+	{x509.ExtKeyUsageNetscapeServerGatedCrypto, oidExtKeyUsageNetscapeServerGatedCrypto},
+	{x509.ExtKeyUsageMicrosoftCommercialCodeSigning, oidExtKeyUsageMicrosoftCommercialCodeSigning},
+	{x509.ExtKeyUsageMicrosoftKernelCodeSigning, oidExtKeyUsageMicrosoftKernelCodeSigning},
+}
+
+func extKeyUsageFromOID(oid asn1.ObjectIdentifier) (eku x509.ExtKeyUsage, ok bool) {
+	for _, pair := range extKeyUsageOIDs {
+		if oid.Equal(pair.oid) {
+			return pair.extKeyUsage, true
+		}
+	}
+	return
+}
+
+func oidFromExtKeyUsage(eku x509.ExtKeyUsage) (oid asn1.ObjectIdentifier, ok bool) {
+	for _, pair := range extKeyUsageOIDs {
+		if eku == pair.extKeyUsage {
+			return pair.oid, true
+		}
+	}
+	return
+}
+
+type basicConstraints struct {
+	IsCA       bool `asn1:"optional"`
+	MaxPathLen int  `asn1:"optional,default:-1"`
+}
+
+// RFC 5280, 4.2.2.1
+type authorityInfoAccess struct {
+	Method   asn1.ObjectIdentifier
+	Location asn1.RawValue
+}
+
+// RFC 5280 4.2.1.4
+type policyInformation struct {
+	Policy asn1.ObjectIdentifier
+	// policyQualifiers omitted
+}
+
+var (
+	oidAuthorityInfoAccessOcsp    = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 48, 1}
+	oidAuthorityInfoAccessIssuers = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 48, 2}
+)
+
+func isIA5String(s string) error {
+	for _, r := range s {
+		if r >= utf8.RuneSelf {
+			return fmt.Errorf("x509: %q cannot be encoded as an IA5String", s)
+		}
+	}
+
+	return nil
+}
+
+type distributionPointName struct {
+	FullName     []asn1.RawValue  `asn1:"optional,tag:0"`
+	RelativeName pkix.RDNSequence `asn1:"optional,tag:1"`
+}
+
+// RFC 5280, 4.2.1.14
+type distributionPoint struct {
+	DistributionPoint distributionPointName `asn1:"optional,tag:0"`
+	Reason            asn1.BitString        `asn1:"optional,tag:1"`
+	CRLIssuer         asn1.RawValue         `asn1:"optional,tag:2"`
+}
+
+func buildExtensions(template *x509.Certificate, subjectIsEmpty bool, authorityKeyId []byte) (ret []pkix.Extension, err error) {
+	ret = make([]pkix.Extension, 10 /* maximum number of elements. */)
+	n := 0
+
+	if template.KeyUsage != 0 &&
+		!oidInExtensions(oidExtensionKeyUsage, template.ExtraExtensions) {
+		ret[n].Id = oidExtensionKeyUsage
+		ret[n].Critical = true
+
+		var a [2]byte
+		a[0] = reverseBitsInAByte(byte(template.KeyUsage))
+		a[1] = reverseBitsInAByte(byte(template.KeyUsage >> 8))
+
+		l := 1
+		if a[1] != 0 {
+			l = 2
+		}
+
+		bitString := a[:l]
+		ret[n].Value, err = asn1.Marshal(asn1.BitString{Bytes: bitString, BitLength: asn1BitLength(bitString)})
+		if err != nil {
+			return
+		}
+		n++
+	}
+
+	if (len(template.ExtKeyUsage) > 0 || len(template.UnknownExtKeyUsage) > 0) &&
+		!oidInExtensions(oidExtensionExtendedKeyUsage, template.ExtraExtensions) {
+		ret[n].Id = oidExtensionExtendedKeyUsage
+
+		var oids []asn1.ObjectIdentifier
+		for _, u := range template.ExtKeyUsage {
+			if oid, ok := oidFromExtKeyUsage(u); ok {
+				oids = append(oids, oid)
+			} else {
+				panic("internal error")
+			}
+		}
+
+		oids = append(oids, template.UnknownExtKeyUsage...)
+
+		ret[n].Value, err = asn1.Marshal(oids)
+		if err != nil {
+			return
+		}
+		n++
+	}
+
+	if template.BasicConstraintsValid && !oidInExtensions(oidExtensionBasicConstraints, template.ExtraExtensions) {
+		// Leaving MaxPathLen as zero indicates that no maximum path
+		// length is desired, unless MaxPathLenZero is set. A value of
+		// -1 causes encoding/asn1 to omit the value as desired.
+		maxPathLen := template.MaxPathLen
+		if maxPathLen == 0 && !template.MaxPathLenZero {
+			maxPathLen = -1
+		}
+		ret[n].Id = oidExtensionBasicConstraints
+		ret[n].Value, err = asn1.Marshal(basicConstraints{template.IsCA, maxPathLen})
+		ret[n].Critical = true
+		if err != nil {
+			return
+		}
+		n++
+	}
+
+	if len(template.SubjectKeyId) > 0 && !oidInExtensions(oidExtensionSubjectKeyId, template.ExtraExtensions) {
+		ret[n].Id = oidExtensionSubjectKeyId
+		ret[n].Value, err = asn1.Marshal(template.SubjectKeyId)
+		if err != nil {
+			return
+		}
+		n++
+	}
+
+	if len(authorityKeyId) > 0 && !oidInExtensions(oidExtensionAuthorityKeyId, template.ExtraExtensions) {
+		ret[n].Id = oidExtensionAuthorityKeyId
+		ret[n].Value, err = asn1.Marshal(authKeyId{authorityKeyId})
+		if err != nil {
+			return
+		}
+		n++
+	}
+
+	if (len(template.OCSPServer) > 0 || len(template.IssuingCertificateURL) > 0) &&
+		!oidInExtensions(oidExtensionAuthorityInfoAccess, template.ExtraExtensions) {
+		ret[n].Id = oidExtensionAuthorityInfoAccess
+		var aiaValues []authorityInfoAccess
+		for _, name := range template.OCSPServer {
+			aiaValues = append(aiaValues, authorityInfoAccess{
+				Method:   oidAuthorityInfoAccessOcsp,
+				Location: asn1.RawValue{Tag: 6, Class: 2, Bytes: []byte(name)},
+			})
+		}
+		for _, name := range template.IssuingCertificateURL {
+			aiaValues = append(aiaValues, authorityInfoAccess{
+				Method:   oidAuthorityInfoAccessIssuers,
+				Location: asn1.RawValue{Tag: 6, Class: 2, Bytes: []byte(name)},
+			})
+		}
+		ret[n].Value, err = asn1.Marshal(aiaValues)
+		if err != nil {
+			return
+		}
+		n++
+	}
+
+	if (len(template.DNSNames) > 0 || len(template.EmailAddresses) > 0 || len(template.IPAddresses) > 0 || len(template.URIs) > 0) &&
+		!oidInExtensions(oidExtensionSubjectAltName, template.ExtraExtensions) {
+		ret[n].Id = oidExtensionSubjectAltName
+		// From RFC 5280, Section 4.2.1.6:
+		// “If the subject field contains an empty sequence ... then
+		// subjectAltName extension ... is marked as critical”
+		ret[n].Critical = subjectIsEmpty
+		ret[n].Value, err = marshalSANs(template.DNSNames, template.EmailAddresses, template.IPAddresses, template.URIs)
+		if err != nil {
+			return
+		}
+		n++
+	}
+
+	if len(template.PolicyIdentifiers) > 0 &&
+		!oidInExtensions(oidExtensionCertificatePolicies, template.ExtraExtensions) {
+		ret[n].Id = oidExtensionCertificatePolicies
+		policies := make([]policyInformation, len(template.PolicyIdentifiers))
+		for i, policy := range template.PolicyIdentifiers {
+			policies[i].Policy = policy
+		}
+		ret[n].Value, err = asn1.Marshal(policies)
+		if err != nil {
+			return
+		}
+		n++
+	}
+
+	if (len(template.PermittedDNSDomains) > 0 || len(template.ExcludedDNSDomains) > 0 ||
+		len(template.PermittedIPRanges) > 0 || len(template.ExcludedIPRanges) > 0 ||
+		len(template.PermittedEmailAddresses) > 0 || len(template.ExcludedEmailAddresses) > 0 ||
+		len(template.PermittedURIDomains) > 0 || len(template.ExcludedURIDomains) > 0) &&
+		!oidInExtensions(oidExtensionNameConstraints, template.ExtraExtensions) {
+		ret[n].Id = oidExtensionNameConstraints
+		ret[n].Critical = template.PermittedDNSDomainsCritical
+
+		ipAndMask := func(ipNet *net.IPNet) []byte {
+			maskedIP := ipNet.IP.Mask(ipNet.Mask)
+			ipAndMask := make([]byte, 0, len(maskedIP)+len(ipNet.Mask))
+			ipAndMask = append(ipAndMask, maskedIP...)
+			ipAndMask = append(ipAndMask, ipNet.Mask...)
+			return ipAndMask
+		}
+
+		serialiseConstraints := func(dns []string, ips []*net.IPNet, emails []string, uriDomains []string) (der []byte, err error) {
+			var b cryptobyte.Builder
+
+			for _, name := range dns {
+				if err = isIA5String(name); err != nil {
+					return nil, err
+				}
+
+				b.AddASN1(cryptobyte_asn1.SEQUENCE, func(b *cryptobyte.Builder) {
+					b.AddASN1(cryptobyte_asn1.Tag(2).ContextSpecific(), func(b *cryptobyte.Builder) {
+						b.AddBytes([]byte(name))
+					})
+				})
+			}
+
+			for _, ipNet := range ips {
+				b.AddASN1(cryptobyte_asn1.SEQUENCE, func(b *cryptobyte.Builder) {
+					b.AddASN1(cryptobyte_asn1.Tag(7).ContextSpecific(), func(b *cryptobyte.Builder) {
+						b.AddBytes(ipAndMask(ipNet))
+					})
+				})
+			}
+
+			for _, email := range emails {
+				if err = isIA5String(email); err != nil {
+					return nil, err
+				}
+
+				b.AddASN1(cryptobyte_asn1.SEQUENCE, func(b *cryptobyte.Builder) {
+					b.AddASN1(cryptobyte_asn1.Tag(1).ContextSpecific(), func(b *cryptobyte.Builder) {
+						b.AddBytes([]byte(email))
+					})
+				})
+			}
+
+			for _, uriDomain := range uriDomains {
+				if err = isIA5String(uriDomain); err != nil {
+					return nil, err
+				}
+
+				b.AddASN1(cryptobyte_asn1.SEQUENCE, func(b *cryptobyte.Builder) {
+					b.AddASN1(cryptobyte_asn1.Tag(6).ContextSpecific(), func(b *cryptobyte.Builder) {
+						b.AddBytes([]byte(uriDomain))
+					})
+				})
+			}
+
+			return b.Bytes()
+		}
+
+		permitted, err := serialiseConstraints(template.PermittedDNSDomains, template.PermittedIPRanges, template.PermittedEmailAddresses, template.PermittedURIDomains)
+		if err != nil {
+			return nil, err
+		}
+
+		excluded, err := serialiseConstraints(template.ExcludedDNSDomains, template.ExcludedIPRanges, template.ExcludedEmailAddresses, template.ExcludedURIDomains)
+		if err != nil {
+			return nil, err
+		}
+
+		var b cryptobyte.Builder
+		b.AddASN1(cryptobyte_asn1.SEQUENCE, func(b *cryptobyte.Builder) {
+			if len(permitted) > 0 {
+				b.AddASN1(cryptobyte_asn1.Tag(0).ContextSpecific().Constructed(), func(b *cryptobyte.Builder) {
+					b.AddBytes(permitted)
+				})
+			}
+
+			if len(excluded) > 0 {
+				b.AddASN1(cryptobyte_asn1.Tag(1).ContextSpecific().Constructed(), func(b *cryptobyte.Builder) {
+					b.AddBytes(excluded)
+				})
+			}
+		})
+
+		ret[n].Value, err = b.Bytes()
+		if err != nil {
+			return nil, err
+		}
+		n++
+	}
+
+	if len(template.CRLDistributionPoints) > 0 &&
+		!oidInExtensions(oidExtensionCRLDistributionPoints, template.ExtraExtensions) {
+		ret[n].Id = oidExtensionCRLDistributionPoints
+
+		var crlDp []distributionPoint
+		for _, name := range template.CRLDistributionPoints {
+			dp := distributionPoint{
+				DistributionPoint: distributionPointName{
+					FullName: []asn1.RawValue{
+						{Tag: 6, Class: 2, Bytes: []byte(name)},
+					},
+				},
+			}
+			crlDp = append(crlDp, dp)
+		}
+
+		ret[n].Value, err = asn1.Marshal(crlDp)
+		if err != nil {
+			return
+		}
+		n++
+	}
+
+	// Adding another extension here? Remember to update the maximum number
+	// of elements in the make() at the top of the function and the list of
+	// template fields used in CreateCertificate documentation.
+
+	return append(ret[:n], template.ExtraExtensions...), nil
+}
+
+func subjectBytes(cert *x509.Certificate) ([]byte, error) {
+	if len(cert.RawSubject) > 0 {
+		return cert.RawSubject, nil
+	}
+
+	return asn1.Marshal(cert.Subject.ToRDNSequence())
+}
+
+// emptyASN1Subject is the ASN.1 DER encoding of an empty Subject, which is
+// just an empty SEQUENCE.
+var emptyASN1Subject = []byte{0x30, 0}
+
+// A Certificate represents an X.509 certificate.
+type Certificate struct {
+	x509.Certificate
+}
+
+func (c *Certificate) Equal(other *Certificate) bool {
+	if c == nil || other == nil {
+		return c == other
+	}
+	return bytes.Equal(c.Raw, other.Raw)
+}
+
+func (c *Certificate) hasNameConstraints() bool {
+	return oidInExtensions(oidExtensionNameConstraints, c.Extensions)
+}
+
+func (c *Certificate) hasSANExtension() bool {
+	return oidInExtensions(oidExtensionSubjectAltName, c.Extensions)
+}
+
+func (c *Certificate) getSANExtension() []byte {
+	for _, e := range c.Extensions {
+		if e.Id.Equal(oidExtensionSubjectAltName) {
+			return e.Value
+		}
+	}
+	return nil
+}
+
+func isRSAPSS(algo x509.SignatureAlgorithm) bool {
+	switch algo {
+	case x509.SHA256WithRSAPSS, x509.SHA384WithRSAPSS, x509.SHA512WithRSAPSS:
+		return true
+	default:
+		return false
+	}
+}
+
+// signingParamsForPublicKey returns the parameters to use for signing with
+// priv. If requestedSigAlgo is not zero then it overrides the default
+// signature algorithm.
+func signingParamsForPublicKey(pub interface{}, requestedSigAlgo x509.SignatureAlgorithm) (hashFunc crypto.Hash, sigAlgo pkix.AlgorithmIdentifier, err error) {
+	var pubType x509.PublicKeyAlgorithm
+
+	switch pub := pub.(type) {
+	case *rsa.PublicKey:
+		pubType = x509.RSA
+		hashFunc = crypto.SHA256
+		sigAlgo.Algorithm = oidSignatureSHA256WithRSA
+		sigAlgo.Parameters = asn1.NullRawValue
+
+	case *ecdsa.PublicKey:
+		pubType = x509.ECDSA
+
+		switch pub.Curve {
+		case elliptic.P224(), elliptic.P256():
+			hashFunc = crypto.SHA256
+			sigAlgo.Algorithm = oidSignatureECDSAWithSHA256
+		case elliptic.P384():
+			hashFunc = crypto.SHA384
+			sigAlgo.Algorithm = oidSignatureECDSAWithSHA384
+		case elliptic.P521():
+			hashFunc = crypto.SHA512
+			sigAlgo.Algorithm = oidSignatureECDSAWithSHA512
+		case sm2.P256():
+			hashFunc = crypto.Hash(0)
+			sigAlgo.Algorithm = oidSignatureSM2WithSM3
+		default:
+			err = errors.New("x509: unknown elliptic curve")
+		}
+
+	case ed25519.PublicKey:
+		pubType = x509.Ed25519
+		sigAlgo.Algorithm = oidSignatureEd25519
+
+	default:
+		err = errors.New("x509: only RSA, ECDSA and Ed25519 keys supported")
+	}
+
+	if err != nil {
+		return
+	}
+
+	if requestedSigAlgo == 0 {
+		return
+	}
+
+	found := false
+	for _, details := range signatureAlgorithmDetails {
+		if details.algo == requestedSigAlgo {
+			if details.pubKeyAlgo != pubType {
+				err = errors.New("x509: requested SignatureAlgorithm does not match private key type")
+				return
+			}
+			sigAlgo.Algorithm, hashFunc = details.oid, details.hash
+			if hashFunc == 0 && pubType != x509.Ed25519 {
+				err = errors.New("x509: cannot sign with hash function requested")
+				return
+			}
+			if isRSAPSS(requestedSigAlgo) {
+				sigAlgo.Parameters = rsaPSSParameters(hashFunc)
+			}
+			found = true
+			break
+		}
+	}
+
+	if !found {
+		err = errors.New("x509: unknown SignatureAlgorithm")
+	}
+
+	return
+}
+
+// CreateCertificate creates a new X.509v3 certificate based on a template.
+// The following members of template are used:
+//
+//  - AuthorityKeyId
+//  - BasicConstraintsValid
+//  - CRLDistributionPoints
+//  - DNSNames
+//  - EmailAddresses
+//  - ExcludedDNSDomains
+//  - ExcludedEmailAddresses
+//  - ExcludedIPRanges
+//  - ExcludedURIDomains
+//  - ExtKeyUsage
+//  - ExtraExtensions
+//  - IPAddresses
+//  - IsCA
+//  - IssuingCertificateURL
+//  - KeyUsage
+//  - MaxPathLen
+//  - MaxPathLenZero
+//  - NotAfter
+//  - NotBefore
+//  - OCSPServer
+//  - PermittedDNSDomains
+//  - PermittedDNSDomainsCritical
+//  - PermittedEmailAddresses
+//  - PermittedIPRanges
+//  - PermittedURIDomains
+//  - PolicyIdentifiers
+//  - SerialNumber
+//  - SignatureAlgorithm
+//  - Subject
+//  - SubjectKeyId
+//  - URIs
+//  - UnknownExtKeyUsage
+//
+// The certificate is signed by parent. If parent is equal to template then the
+// certificate is self-signed. The parameter pub is the public key of the
+// signee and priv is the private key of the signer.
+//
+// The returned slice is the certificate in DER encoding.
+//
+// The currently supported key types are *rsa.PublicKey, *ecdsa.PublicKey and
+// ed25519.PublicKey. pub must be a supported key type, and priv must be a
+// crypto.Signer with a supported public key.
+//
+// The AuthorityKeyId will be taken from the SubjectKeyId of parent, if any,
+// unless the resulting certificate is self-signed. Otherwise the value from
+// template will be used.
+func CreateCertificate(rand io.Reader, template, parent *x509.Certificate, pub, priv interface{}) (cert []byte, err error) {
+	key, ok := priv.(crypto.Signer)
+	if !ok {
+		return nil, errors.New("x509: certificate private key does not implement crypto.Signer")
+	}
+	hashFunc, signatureAlgorithm, err := signingParamsForPublicKey(key.Public(), template.SignatureAlgorithm)
+	if err != nil {
+		return nil, err
+	}
+	if template.SerialNumber == nil {
+		return nil, errors.New("x509: no SerialNumber given")
+	}
+	publicKeyBytes, publicKeyAlgorithm, err := marshalPublicKey(pub)
+	if err != nil {
+		return nil, err
+	}
+
+	asn1Issuer, err := subjectBytes(parent)
+	if err != nil {
+		return
+	}
+
+	asn1Subject, err := subjectBytes(template)
+	if err != nil {
+		return
+	}
+
+	authorityKeyId := template.AuthorityKeyId
+	if !bytes.Equal(asn1Issuer, asn1Subject) && len(parent.SubjectKeyId) > 0 {
+		authorityKeyId = parent.SubjectKeyId
+	}
+
+	extensions, err := buildExtensions(template, bytes.Equal(asn1Subject, emptyASN1Subject), authorityKeyId)
+	if err != nil {
+		return
+	}
+
+	encodedPublicKey := asn1.BitString{BitLength: len(publicKeyBytes) * 8, Bytes: publicKeyBytes}
+	c := tbsCertificate{
+		Version:            2,
+		SerialNumber:       template.SerialNumber,
+		SignatureAlgorithm: signatureAlgorithm,
+		Issuer:             asn1.RawValue{FullBytes: asn1Issuer},
+		Validity:           validity{template.NotBefore.UTC(), template.NotAfter.UTC()},
+		Subject:            asn1.RawValue{FullBytes: asn1Subject},
+		PublicKey:          publicKeyInfo{nil, publicKeyAlgorithm, encodedPublicKey},
+		Extensions:         extensions,
+	}
+
+	tbsCertContents, err := asn1.Marshal(c)
+	if err != nil {
+		return
+	}
+	c.Raw = tbsCertContents
+
+	signed := tbsCertContents
+
+	var signature []byte
+	if signatureAlgorithm.Algorithm.Equal(oidSignatureSM2WithSM3) {
+		privKey, ok := key.(*sm2.PrivateKey)
+		if !ok {
+			ecKey, ok := key.(*ecdsa.PrivateKey)
+			if ok && ecKey.Curve == sm2.P256() {
+				privKey, _ = new(sm2.PrivateKey).FromECPrivateKey(ecKey)
+			}
+		}
+		signature, err = privKey.SignWithSM2(rand, nil, signed)
+	} else {
+		if hashFunc != 0 {
+			h := hashFunc.New()
+			h.Write(signed)
+			signed = h.Sum(nil)
+		}
+
+		var signerOpts crypto.SignerOpts = hashFunc
+		if template.SignatureAlgorithm != 0 && isRSAPSS(template.SignatureAlgorithm) {
+			signerOpts = &rsa.PSSOptions{
+				SaltLength: rsa.PSSSaltLengthEqualsHash,
+				Hash:       hashFunc,
+			}
+		}
+
+		signature, err = key.Sign(rand, signed, signerOpts)
+	}
+	if err != nil {
+		return
+	}
+
+	return asn1.Marshal(certificate{
+		nil,
+		c,
+		signatureAlgorithm,
+		asn1.BitString{Bytes: signature, BitLength: len(signature) * 8},
+	})
+}
+
+// isValidIPMask reports whether mask consists of zero or more 1 bits, followed by zero bits.
+func isValidIPMask(mask []byte) bool {
+	seenZero := false
+
+	for _, b := range mask {
+		if seenZero {
+			if b != 0 {
+				return false
+			}
+
+			continue
+		}
+
+		switch b {
+		case 0x00, 0x80, 0xc0, 0xe0, 0xf0, 0xf8, 0xfc, 0xfe:
+			seenZero = true
+		case 0xff:
+		default:
+			return false
+		}
+	}
+
+	return true
+}
+
+func parseNameConstraintsExtension(out *x509.Certificate, e pkix.Extension) (unhandled bool, err error) {
+	// RFC 5280, 4.2.1.10
+
+	// NameConstraints ::= SEQUENCE {
+	//      permittedSubtrees       [0]     GeneralSubtrees OPTIONAL,
+	//      excludedSubtrees        [1]     GeneralSubtrees OPTIONAL }
+	//
+	// GeneralSubtrees ::= SEQUENCE SIZE (1..MAX) OF GeneralSubtree
+	//
+	// GeneralSubtree ::= SEQUENCE {
+	//      base                    GeneralName,
+	//      minimum         [0]     BaseDistance DEFAULT 0,
+	//      maximum         [1]     BaseDistance OPTIONAL }
+	//
+	// BaseDistance ::= INTEGER (0..MAX)
+
+	outer := cryptobyte.String(e.Value)
+	var toplevel, permitted, excluded cryptobyte.String
+	var havePermitted, haveExcluded bool
+	if !outer.ReadASN1(&toplevel, cryptobyte_asn1.SEQUENCE) ||
+		!outer.Empty() ||
+		!toplevel.ReadOptionalASN1(&permitted, &havePermitted, cryptobyte_asn1.Tag(0).ContextSpecific().Constructed()) ||
+		!toplevel.ReadOptionalASN1(&excluded, &haveExcluded, cryptobyte_asn1.Tag(1).ContextSpecific().Constructed()) ||
+		!toplevel.Empty() {
+		return false, errors.New("x509: invalid NameConstraints extension")
+	}
+
+	if !havePermitted && !haveExcluded || len(permitted) == 0 && len(excluded) == 0 {
+		// From RFC 5280, Section 4.2.1.10:
+		//   “either the permittedSubtrees field
+		//   or the excludedSubtrees MUST be
+		//   present”
+		return false, errors.New("x509: empty name constraints extension")
+	}
+
+	getValues := func(subtrees cryptobyte.String) (dnsNames []string, ips []*net.IPNet, emails, uriDomains []string, err error) {
+		for !subtrees.Empty() {
+			var seq, value cryptobyte.String
+			var tag cryptobyte_asn1.Tag
+			if !subtrees.ReadASN1(&seq, cryptobyte_asn1.SEQUENCE) ||
+				!seq.ReadAnyASN1(&value, &tag) {
+				return nil, nil, nil, nil, fmt.Errorf("x509: invalid NameConstraints extension")
+			}
+
+			var (
+				dnsTag   = cryptobyte_asn1.Tag(2).ContextSpecific()
+				emailTag = cryptobyte_asn1.Tag(1).ContextSpecific()
+				ipTag    = cryptobyte_asn1.Tag(7).ContextSpecific()
+				uriTag   = cryptobyte_asn1.Tag(6).ContextSpecific()
+			)
+
+			switch tag {
+			case dnsTag:
+				domain := string(value)
+				if err := isIA5String(domain); err != nil {
+					return nil, nil, nil, nil, errors.New("x509: invalid constraint value: " + err.Error())
+				}
+
+				trimmedDomain := domain
+				if len(trimmedDomain) > 0 && trimmedDomain[0] == '.' {
+					// constraints can have a leading
+					// period to exclude the domain
+					// itself, but that's not valid in a
+					// normal domain name.
+					trimmedDomain = trimmedDomain[1:]
+				}
+				if _, ok := domainToReverseLabels(trimmedDomain); !ok {
+					return nil, nil, nil, nil, fmt.Errorf("x509: failed to parse dnsName constraint %q", domain)
+				}
+				dnsNames = append(dnsNames, domain)
+
+			case ipTag:
+				l := len(value)
+				var ip, mask []byte
+
+				switch l {
+				case 8:
+					ip = value[:4]
+					mask = value[4:]
+
+				case 32:
+					ip = value[:16]
+					mask = value[16:]
+
+				default:
+					return nil, nil, nil, nil, fmt.Errorf("x509: IP constraint contained value of length %d", l)
+				}
+
+				if !isValidIPMask(mask) {
+					return nil, nil, nil, nil, fmt.Errorf("x509: IP constraint contained invalid mask %x", mask)
+				}
+
+				ips = append(ips, &net.IPNet{IP: net.IP(ip), Mask: net.IPMask(mask)})
+
+			case emailTag:
+				constraint := string(value)
+				if err := isIA5String(constraint); err != nil {
+					return nil, nil, nil, nil, errors.New("x509: invalid constraint value: " + err.Error())
+				}
+
+				// If the constraint contains an @ then
+				// it specifies an exact mailbox name.
+				if strings.Contains(constraint, "@") {
+					if _, ok := parseRFC2821Mailbox(constraint); !ok {
+						return nil, nil, nil, nil, fmt.Errorf("x509: failed to parse rfc822Name constraint %q", constraint)
+					}
+				} else {
+					// Otherwise it's a domain name.
+					domain := constraint
+					if len(domain) > 0 && domain[0] == '.' {
+						domain = domain[1:]
+					}
+					if _, ok := domainToReverseLabels(domain); !ok {
+						return nil, nil, nil, nil, fmt.Errorf("x509: failed to parse rfc822Name constraint %q", constraint)
+					}
+				}
+				emails = append(emails, constraint)
+
+			case uriTag:
+				domain := string(value)
+				if err := isIA5String(domain); err != nil {
+					return nil, nil, nil, nil, errors.New("x509: invalid constraint value: " + err.Error())
+				}
+
+				if net.ParseIP(domain) != nil {
+					return nil, nil, nil, nil, fmt.Errorf("x509: failed to parse URI constraint %q: cannot be IP address", domain)
+				}
+
+				trimmedDomain := domain
+				if len(trimmedDomain) > 0 && trimmedDomain[0] == '.' {
+					// constraints can have a leading
+					// period to exclude the domain itself,
+					// but that's not valid in a normal
+					// domain name.
+					trimmedDomain = trimmedDomain[1:]
+				}
+				if _, ok := domainToReverseLabels(trimmedDomain); !ok {
+					return nil, nil, nil, nil, fmt.Errorf("x509: failed to parse URI constraint %q", domain)
+				}
+				uriDomains = append(uriDomains, domain)
+
+			default:
+				unhandled = true
+			}
+		}
+
+		return dnsNames, ips, emails, uriDomains, nil
+	}
+
+	if out.PermittedDNSDomains, out.PermittedIPRanges, out.PermittedEmailAddresses, out.PermittedURIDomains, err = getValues(permitted); err != nil {
+		return false, err
+	}
+	if out.ExcludedDNSDomains, out.ExcludedIPRanges, out.ExcludedEmailAddresses, out.ExcludedURIDomains, err = getValues(excluded); err != nil {
+		return false, err
+	}
+	out.PermittedDNSDomainsCritical = e.Critical
+
+	return unhandled, nil
+}
+
+func getSignatureAlgorithmFromAI(ai pkix.AlgorithmIdentifier) x509.SignatureAlgorithm {
+	if ai.Algorithm.Equal(oidSignatureEd25519) {
+		// RFC 8410, Section 3
+		// > For all of the OIDs, the parameters MUST be absent.
+		if len(ai.Parameters.FullBytes) != 0 {
+			return x509.UnknownSignatureAlgorithm
+		}
+	}
+
+	if !ai.Algorithm.Equal(oidSignatureRSAPSS) {
+		for _, details := range signatureAlgorithmDetails {
+			if ai.Algorithm.Equal(details.oid) {
+				return details.algo
+			}
+		}
+		return x509.UnknownSignatureAlgorithm
+	}
+
+	// RSA PSS is special because it encodes important parameters
+	// in the Parameters.
+
+	var params pssParameters
+	if _, err := asn1.Unmarshal(ai.Parameters.FullBytes, &params); err != nil {
+		return x509.UnknownSignatureAlgorithm
+	}
+
+	var mgf1HashFunc pkix.AlgorithmIdentifier
+	if _, err := asn1.Unmarshal(params.MGF.Parameters.FullBytes, &mgf1HashFunc); err != nil {
+		return x509.UnknownSignatureAlgorithm
+	}
+
+	// PSS is greatly overburdened with options. This code forces them into
+	// three buckets by requiring that the MGF1 hash function always match the
+	// message hash function (as recommended in RFC 3447, Section 8.1), that the
+	// salt length matches the hash length, and that the trailer field has the
+	// default value.
+	if (len(params.Hash.Parameters.FullBytes) != 0 && !bytes.Equal(params.Hash.Parameters.FullBytes, asn1.NullBytes)) ||
+		!params.MGF.Algorithm.Equal(oidMGF1) ||
+		!mgf1HashFunc.Algorithm.Equal(params.Hash.Algorithm) ||
+		(len(mgf1HashFunc.Parameters.FullBytes) != 0 && !bytes.Equal(mgf1HashFunc.Parameters.FullBytes, asn1.NullBytes)) ||
+		params.TrailerField != 1 {
+		return x509.UnknownSignatureAlgorithm
+	}
+
+	switch {
+	case params.Hash.Algorithm.Equal(oidSHA256) && params.SaltLength == 32:
+		return x509.SHA256WithRSAPSS
+	case params.Hash.Algorithm.Equal(oidSHA384) && params.SaltLength == 48:
+		return x509.SHA384WithRSAPSS
+	case params.Hash.Algorithm.Equal(oidSHA512) && params.SaltLength == 64:
+		return x509.SHA512WithRSAPSS
+	}
+
+	return x509.UnknownSignatureAlgorithm
+}
+
+func parseCertificate(in *certificate) (*x509.Certificate, error) {
+	out := new(x509.Certificate)
+	out.Raw = in.Raw
+	out.RawTBSCertificate = in.TBSCertificate.Raw
+	out.RawSubjectPublicKeyInfo = in.TBSCertificate.PublicKey.Raw
+	out.RawSubject = in.TBSCertificate.Subject.FullBytes
+	out.RawIssuer = in.TBSCertificate.Issuer.FullBytes
+
+	out.Signature = in.SignatureValue.RightAlign()
+	out.SignatureAlgorithm = getSignatureAlgorithmFromAI(in.TBSCertificate.SignatureAlgorithm)
+
+	out.PublicKeyAlgorithm =
+		getPublicKeyAlgorithmFromOID(in.TBSCertificate.PublicKey.Algorithm.Algorithm)
+	var err error
+	out.PublicKey, err = parsePublicKey(out.PublicKeyAlgorithm, &in.TBSCertificate.PublicKey)
+	if err != nil {
+		return nil, err
+	}
+
+	out.Version = in.TBSCertificate.Version + 1
+	out.SerialNumber = in.TBSCertificate.SerialNumber
+
+	var issuer, subject pkix.RDNSequence
+	if rest, err := asn1.Unmarshal(in.TBSCertificate.Subject.FullBytes, &subject); err != nil {
+		return nil, err
+	} else if len(rest) != 0 {
+		return nil, errors.New("x509: trailing data after X.509 subject")
+	}
+	if rest, err := asn1.Unmarshal(in.TBSCertificate.Issuer.FullBytes, &issuer); err != nil {
+		return nil, err
+	} else if len(rest) != 0 {
+		return nil, errors.New("x509: trailing data after X.509 subject")
+	}
+
+	out.Issuer.FillFromRDNSequence(&issuer)
+	out.Subject.FillFromRDNSequence(&subject)
+
+	out.NotBefore = in.TBSCertificate.Validity.NotBefore
+	out.NotAfter = in.TBSCertificate.Validity.NotAfter
+
+	for _, e := range in.TBSCertificate.Extensions {
+		out.Extensions = append(out.Extensions, e)
+		unhandled := false
+
+		if len(e.Id) == 4 && e.Id[0] == 2 && e.Id[1] == 5 && e.Id[2] == 29 {
+			switch e.Id[3] {
+			case 15:
+				// RFC 5280, 4.2.1.3
+				var usageBits asn1.BitString
+				if rest, err := asn1.Unmarshal(e.Value, &usageBits); err != nil {
+					return nil, err
+				} else if len(rest) != 0 {
+					return nil, errors.New("x509: trailing data after X.509 KeyUsage")
+				}
+
+				var usage int
+				for i := 0; i < 9; i++ {
+					if usageBits.At(i) != 0 {
+						usage |= 1 << uint(i)
+					}
+				}
+				out.KeyUsage = x509.KeyUsage(usage)
+
+			case 19:
+				// RFC 5280, 4.2.1.9
+				var constraints basicConstraints
+				if rest, err := asn1.Unmarshal(e.Value, &constraints); err != nil {
+					return nil, err
+				} else if len(rest) != 0 {
+					return nil, errors.New("x509: trailing data after X.509 BasicConstraints")
+				}
+
+				out.BasicConstraintsValid = true
+				out.IsCA = constraints.IsCA
+				out.MaxPathLen = constraints.MaxPathLen
+				out.MaxPathLenZero = out.MaxPathLen == 0
+				// TODO: map out.MaxPathLen to 0 if it has the -1 default value? (Issue 19285)
+			case 17:
+				out.DNSNames, out.EmailAddresses, out.IPAddresses, out.URIs, err = parseSANExtension(e.Value)
+				if err != nil {
+					return nil, err
+				}
+
+				if len(out.DNSNames) == 0 && len(out.EmailAddresses) == 0 && len(out.IPAddresses) == 0 && len(out.URIs) == 0 {
+					// If we didn't parse anything then we do the critical check, below.
+					unhandled = true
+				}
+
+			case 30:
+				unhandled, err = parseNameConstraintsExtension(out, e)
+				if err != nil {
+					return nil, err
+				}
+
+			case 31:
+				// RFC 5280, 4.2.1.13
+
+				// CRLDistributionPoints ::= SEQUENCE SIZE (1..MAX) OF DistributionPoint
+				//
+				// DistributionPoint ::= SEQUENCE {
+				//     distributionPoint       [0]     DistributionPointName OPTIONAL,
+				//     reasons                 [1]     ReasonFlags OPTIONAL,
+				//     cRLIssuer               [2]     GeneralNames OPTIONAL }
+				//
+				// DistributionPointName ::= CHOICE {
+				//     fullName                [0]     GeneralNames,
+				//     nameRelativeToCRLIssuer [1]     RelativeDistinguishedName }
+
+				var cdp []distributionPoint
+				if rest, err := asn1.Unmarshal(e.Value, &cdp); err != nil {
+					return nil, err
+				} else if len(rest) != 0 {
+					return nil, errors.New("x509: trailing data after X.509 CRL distribution point")
+				}
+
+				for _, dp := range cdp {
+					// Per RFC 5280, 4.2.1.13, one of distributionPoint or cRLIssuer may be empty.
+					if len(dp.DistributionPoint.FullName) == 0 {
+						continue
+					}
+
+					for _, fullName := range dp.DistributionPoint.FullName {
+						if fullName.Tag == 6 {
+							out.CRLDistributionPoints = append(out.CRLDistributionPoints, string(fullName.Bytes))
+						}
+					}
+				}
+
+			case 35:
+				// RFC 5280, 4.2.1.1
+				var a authKeyId
+				if rest, err := asn1.Unmarshal(e.Value, &a); err != nil {
+					return nil, err
+				} else if len(rest) != 0 {
+					return nil, errors.New("x509: trailing data after X.509 authority key-id")
+				}
+				out.AuthorityKeyId = a.Id
+
+			case 37:
+				// RFC 5280, 4.2.1.12.  Extended Key Usage
+
+				// id-ce-extKeyUsage OBJECT IDENTIFIER ::= { id-ce 37 }
+				//
+				// ExtKeyUsageSyntax ::= SEQUENCE SIZE (1..MAX) OF KeyPurposeId
+				//
+				// KeyPurposeId ::= OBJECT IDENTIFIER
+
+				var keyUsage []asn1.ObjectIdentifier
+				if rest, err := asn1.Unmarshal(e.Value, &keyUsage); err != nil {
+					return nil, err
+				} else if len(rest) != 0 {
+					return nil, errors.New("x509: trailing data after X.509 ExtendedKeyUsage")
+				}
+
+				for _, u := range keyUsage {
+					if extKeyUsage, ok := extKeyUsageFromOID(u); ok {
+						out.ExtKeyUsage = append(out.ExtKeyUsage, extKeyUsage)
+					} else {
+						out.UnknownExtKeyUsage = append(out.UnknownExtKeyUsage, u)
+					}
+				}
+
+			case 14:
+				// RFC 5280, 4.2.1.2
+				var keyid []byte
+				if rest, err := asn1.Unmarshal(e.Value, &keyid); err != nil {
+					return nil, err
+				} else if len(rest) != 0 {
+					return nil, errors.New("x509: trailing data after X.509 key-id")
+				}
+				out.SubjectKeyId = keyid
+
+			case 32:
+				// RFC 5280 4.2.1.4: Certificate Policies
+				var policies []policyInformation
+				if rest, err := asn1.Unmarshal(e.Value, &policies); err != nil {
+					return nil, err
+				} else if len(rest) != 0 {
+					return nil, errors.New("x509: trailing data after X.509 certificate policies")
+				}
+				out.PolicyIdentifiers = make([]asn1.ObjectIdentifier, len(policies))
+				for i, policy := range policies {
+					out.PolicyIdentifiers[i] = policy.Policy
+				}
+
+			default:
+				// Unknown extensions are recorded if critical.
+				unhandled = true
+			}
+		} else if e.Id.Equal(oidExtensionAuthorityInfoAccess) {
+			// RFC 5280 4.2.2.1: Authority Information Access
+			var aia []authorityInfoAccess
+			if rest, err := asn1.Unmarshal(e.Value, &aia); err != nil {
+				return nil, err
+			} else if len(rest) != 0 {
+				return nil, errors.New("x509: trailing data after X.509 authority information")
+			}
+
+			for _, v := range aia {
+				// GeneralName: uniformResourceIdentifier [6] IA5String
+				if v.Location.Tag != 6 {
+					continue
+				}
+				if v.Method.Equal(oidAuthorityInfoAccessOcsp) {
+					out.OCSPServer = append(out.OCSPServer, string(v.Location.Bytes))
+				} else if v.Method.Equal(oidAuthorityInfoAccessIssuers) {
+					out.IssuingCertificateURL = append(out.IssuingCertificateURL, string(v.Location.Bytes))
+				}
+			}
+		} else {
+			// Unknown extensions are recorded if critical.
+			unhandled = true
+		}
+
+		if e.Critical && unhandled {
+			out.UnhandledCriticalExtensions = append(out.UnhandledCriticalExtensions, e.Id)
+		}
+	}
+
+	return out, nil
+}
+
+// ParseCertificate parses a single certificate from the given ASN.1 DER data.
+func ParseCertificate(asn1Data []byte) (*Certificate, error) {
+	var cert certificate
+	rest, err := asn1.Unmarshal(asn1Data, &cert)
+	if err != nil {
+		return nil, err
+	}
+	if len(rest) > 0 {
+		return nil, asn1.SyntaxError{Msg: "trailing data"}
+	}
+
+	var result *x509.Certificate
+	result, err = parseCertificate(&cert)
+
+	if err != nil {
+		return nil, err
+	}
+	return &Certificate{*result}, nil
+}
+
+// ParseCertificates parses one or more certificates from the given ASN.1 DER
+// data. The certificates must be concatenated with no intermediate padding.
+func ParseCertificates(asn1Data []byte) ([]*Certificate, error) {
+	var v []*certificate
+
+	for len(asn1Data) > 0 {
+		cert := new(certificate)
+		var err error
+		asn1Data, err = asn1.Unmarshal(asn1Data, cert)
+		if err != nil {
+			return nil, err
+		}
+		v = append(v, cert)
+	}
+
+	ret := make([]*Certificate, len(v))
+	for i, ci := range v {
+		cert, err := parseCertificate(ci)
+		if err != nil {
+			return nil, err
+		}
+		ret[i] = &Certificate{*cert}
+	}
+
+	return ret, nil
+}
+
+// CheckSignatureFrom verifies that the signature on c is a valid signature
+// from parent.
+func (c *Certificate) CheckSignatureFrom(parent *Certificate) error {
+	// RFC 5280, 4.2.1.9:
+	// "If the basic constraints extension is not present in a version 3
+	// certificate, or the extension is present but the cA boolean is not
+	// asserted, then the certified public key MUST NOT be used to verify
+	// certificate signatures."
+	if parent.Version == 3 && !parent.BasicConstraintsValid ||
+		parent.BasicConstraintsValid && !parent.IsCA {
+		return x509.ConstraintViolationError{}
+	}
+
+	if parent.KeyUsage != 0 && parent.KeyUsage&x509.KeyUsageCertSign == 0 {
+		return x509.ConstraintViolationError{}
+	}
+
+	if parent.PublicKeyAlgorithm == x509.UnknownPublicKeyAlgorithm {
+		return x509.ErrUnsupportedAlgorithm
+	}
+
+	// TODO(agl): don't ignore the path length constraint.
+
+	return parent.CheckSignature(c.SignatureAlgorithm, c.RawTBSCertificate, c.Signature)
+}
+
+// CheckSignature verifies that signature is a valid signature over signed from
+// c's public key.
+func (c *Certificate) CheckSignature(algo x509.SignatureAlgorithm, signed, signature []byte) error {
+	key, ok := c.PublicKey.(*ecdsa.PublicKey)
+	if !ok {
+		return c.Certificate.CheckSignature(algo, signed, signature)
+	}
+	if key.Curve != sm2.P256() {
+		return c.Certificate.CheckSignature(algo, signed, signature)
+	}
+	ecdsaSig := new(ecdsaSignature)
+	if rest, err := asn1.Unmarshal(signature, ecdsaSig); err != nil {
+		return err
+	} else if len(rest) != 0 {
+		return errors.New("x509: trailing data after ECDSA signature")
+	}
+	if ecdsaSig.R.Sign() <= 0 || ecdsaSig.S.Sign() <= 0 {
+		return errors.New("x509: ECDSA signature contained zero or negative values")
+	}
+	if !sm2.VerifyWithSM2(key, nil, signed, ecdsaSig.R, ecdsaSig.S) {
+		return errors.New("x509: ECDSA verification failure")
+	}
+	return nil
+}
+
+// CreateCRL returns a DER encoded CRL, signed by this Certificate, that
+// contains the given list of revoked certificates.
+func (c *Certificate) CreateCRL(rand io.Reader, priv interface{}, revokedCerts []pkix.RevokedCertificate, now, expiry time.Time) (crlBytes []byte, err error) {
+	key, ok := priv.(crypto.Signer)
+	if !ok {
+		return nil, errors.New("x509: certificate private key does not implement crypto.Signer")
+	}
+
+	hashFunc, signatureAlgorithm, err := signingParamsForPublicKey(key.Public(), 0)
+	if err != nil {
+		return nil, err
+	}
+
+	// Force revocation times to UTC per RFC 5280.
+	revokedCertsUTC := make([]pkix.RevokedCertificate, len(revokedCerts))
+	for i, rc := range revokedCerts {
+		rc.RevocationTime = rc.RevocationTime.UTC()
+		revokedCertsUTC[i] = rc
+	}
+
+	tbsCertList := pkix.TBSCertificateList{
+		Version:             1,
+		Signature:           signatureAlgorithm,
+		Issuer:              c.Subject.ToRDNSequence(),
+		ThisUpdate:          now.UTC(),
+		NextUpdate:          expiry.UTC(),
+		RevokedCertificates: revokedCertsUTC,
+	}
+
+	// Authority Key Id
+	if len(c.SubjectKeyId) > 0 {
+		var aki pkix.Extension
+		aki.Id = oidExtensionAuthorityKeyId
+		aki.Value, err = asn1.Marshal(authKeyId{Id: c.SubjectKeyId})
+		if err != nil {
+			return
+		}
+		tbsCertList.Extensions = append(tbsCertList.Extensions, aki)
+	}
+
+	tbsCertListContents, err := asn1.Marshal(tbsCertList)
+	if err != nil {
+		return
+	}
+
+	signed := tbsCertListContents
+	var signature []byte
+	if signatureAlgorithm.Algorithm.Equal(oidSignatureSM2WithSM3) {
+		privKey, ok := key.(*sm2.PrivateKey)
+		if !ok {
+			ecKey, ok := key.(*ecdsa.PrivateKey)
+			if ok && ecKey.Curve == sm2.P256() {
+				privKey, _ = new(sm2.PrivateKey).FromECPrivateKey(ecKey)
+			}
+		}
+		signature, err = privKey.SignWithSM2(rand, nil, signed)
+	} else {
+		if hashFunc != 0 {
+			h := hashFunc.New()
+			h.Write(signed)
+			signed = h.Sum(nil)
+		}
+		signature, err = key.Sign(rand, signed, hashFunc)
+	}
+	if err != nil {
+		return
+	}
+
+	return asn1.Marshal(pkix.CertificateList{
+		TBSCertList:        tbsCertList,
+		SignatureAlgorithm: signatureAlgorithm,
+		SignatureValue:     asn1.BitString{Bytes: signature, BitLength: len(signature) * 8},
+	})
+}
diff --git a/smx509/x509_test.go b/smx509/x509_test.go
index ab6d381..751f452 100644
--- a/smx509/x509_test.go
+++ b/smx509/x509_test.go
@@ -1,8 +1,12 @@
 package smx509
 
 import (
+	"bytes"
 	"crypto/ecdsa"
+	"crypto/ed25519"
+	"crypto/elliptic"
 	"crypto/rand"
+	"crypto/rsa"
 	"crypto/x509"
 	"crypto/x509/pkix"
 	"encoding/asn1"
@@ -11,8 +15,13 @@ import (
 	"encoding/pem"
 	"errors"
 	"fmt"
+	"math/big"
+	"net"
+	"net/url"
+	"reflect"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/emmansun/gmsm/sm2"
 )
@@ -43,6 +52,108 @@ bxIHjKZHc2sztHCXe7cseWGiLq0syg==
 -----END CERTIFICATE REQUEST-----
 `
 
+const pemCertificate = `-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----`
+
+var pemPrivateKey = testingKey(`
+-----BEGIN RSA TESTING KEY-----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+-----END RSA TESTING KEY-----
+`)
+
+const ed25519CRLKey = `-----BEGIN PRIVATE KEY-----
+MC4CAQAwBQYDK2VwBCIEINdKh2096vUBYu4EIFpjShsUSh3vimKya1sQ1YTT4RZG
+-----END PRIVATE KEY-----`
+
+const ed25519CRLCertificate = `
+Certificate:
+Data:
+	Version: 3 (0x2)
+	Serial Number:
+		7a:07:a0:9d:14:04:16:fc:1f:d8:e5:fe:d1:1d:1f:8d
+	Signature Algorithm: ED25519
+	Issuer: CN = Ed25519 CRL Test CA
+	Validity
+		Not Before: Oct 30 01:20:20 2019 GMT
+		Not After : Dec 31 23:59:59 9999 GMT
+	Subject: CN = Ed25519 CRL Test CA
+	Subject Public Key Info:
+		Public Key Algorithm: ED25519
+			ED25519 Public-Key:
+			pub:
+				95:73:3b:b0:06:2a:31:5a:b6:a7:a6:6e:ef:71:df:
+				ac:6f:6b:39:03:85:5e:63:4b:f8:a6:0f:68:c6:6f:
+				75:21
+	X509v3 extensions:
+		X509v3 Key Usage: critical
+			Digital Signature, Certificate Sign, CRL Sign
+		X509v3 Extended Key Usage: 
+			TLS Web Client Authentication, TLS Web Server Authentication, OCSP Signing
+		X509v3 Basic Constraints: critical
+			CA:TRUE
+		X509v3 Subject Key Identifier: 
+			B7:17:DA:16:EA:C5:ED:1F:18:49:44:D3:D2:E3:A0:35:0A:81:93:60
+		X509v3 Authority Key Identifier: 
+			keyid:B7:17:DA:16:EA:C5:ED:1F:18:49:44:D3:D2:E3:A0:35:0A:81:93:60
+Signature Algorithm: ED25519
+	 fc:3e:14:ea:bb:70:c2:6f:38:34:70:bc:c8:a7:f4:7c:0d:1e:
+	 28:d7:2a:9f:22:8a:45:e8:02:76:84:1e:2d:64:2d:1e:09:b5:
+	 29:71:1f:95:8a:4e:79:87:51:60:9a:e7:86:40:f6:60:c7:d1:
+	 ee:68:76:17:1d:90:cc:92:93:07
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----`
+
+var testPrivateKey *rsa.PrivateKey
+
+func init() {
+	block, _ := pem.Decode([]byte(pemPrivateKey))
+
+	var err error
+	if testPrivateKey, err = x509.ParsePKCS1PrivateKey(block.Bytes); err != nil {
+		panic("Failed to parse private key: " + err.Error())
+	}
+}
+
+func testingKey(s string) string { return strings.ReplaceAll(s, "TESTING KEY", "PRIVATE KEY") }
+
 func getPublicKey(pemContent []byte) (interface{}, error) {
 	block, _ := pem.Decode(pemContent)
 	if block == nil {
@@ -57,7 +168,7 @@ func parseAndCheckCsr(csrblock []byte) error {
 		return err
 	}
 	fmt.Printf("%v\n", csr)
-	return CheckSignature(csr)
+	return csr.CheckSignature()
 }
 
 func TestParseCertificateRequest(t *testing.T) {
@@ -73,6 +184,7 @@ func TestParseCertificateRequest(t *testing.T) {
 
 func TestCreateCertificateRequest(t *testing.T) {
 	priv, _ := sm2.GenerateKey(rand.Reader)
+
 	names := pkix.Name{CommonName: "TestName"}
 	var template = x509.CertificateRequest{Subject: names}
 	csrblock, err := CreateCertificateRequest(rand.Reader, &template, priv)
@@ -140,3 +252,420 @@ func TestMarshalPKIXPublicKey(t *testing.T) {
 		t.Errorf("expected=%s, result=%s", publicKeyPemFromAliKms, pemContent)
 	}
 }
+
+func Test_CreateCertificateRequest(t *testing.T) {
+	random := rand.Reader
+
+	sm2Priv, err := sm2.GenerateKey(rand.Reader)
+	if err != nil {
+		t.Fatalf("Failed to generate SM2 key: %s", err)
+	}
+
+	ecdsa256Priv, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	if err != nil {
+		t.Fatalf("Failed to generate ECDSA key: %s", err)
+	}
+
+	ecdsa384Priv, err := ecdsa.GenerateKey(elliptic.P384(), rand.Reader)
+	if err != nil {
+		t.Fatalf("Failed to generate ECDSA key: %s", err)
+	}
+
+	ecdsa521Priv, err := ecdsa.GenerateKey(elliptic.P521(), rand.Reader)
+	if err != nil {
+		t.Fatalf("Failed to generate ECDSA key: %s", err)
+	}
+
+	_, ed25519Priv, err := ed25519.GenerateKey(random)
+	if err != nil {
+		t.Fatalf("Failed to generate Ed25519 key: %s", err)
+	}
+
+	tests := []struct {
+		name    string
+		priv    interface{}
+		sigAlgo x509.SignatureAlgorithm
+	}{
+		{"RSA", testPrivateKey, x509.SHA1WithRSA},
+		{"SM2-256", sm2Priv, -1},
+		{"ECDSA-256", ecdsa256Priv, x509.ECDSAWithSHA1},
+		{"ECDSA-384", ecdsa384Priv, x509.ECDSAWithSHA1},
+		{"ECDSA-521", ecdsa521Priv, x509.ECDSAWithSHA1},
+		{"Ed25519", ed25519Priv, x509.PureEd25519},
+	}
+
+	for _, test := range tests {
+		template := x509.CertificateRequest{
+			Subject: pkix.Name{
+				CommonName:   "test.example.com",
+				Organization: []string{"Σ Acme Co"},
+			},
+			SignatureAlgorithm: test.sigAlgo,
+			DNSNames:           []string{"test.example.com"},
+			EmailAddresses:     []string{"gopher@golang.org"},
+			IPAddresses:        []net.IP{net.IPv4(127, 0, 0, 1).To4(), net.ParseIP("2001:4860:0:2001::68")},
+		}
+
+		derBytes, err := CreateCertificateRequest(random, &template, test.priv)
+		if err != nil {
+			t.Errorf("%s: failed to create certificate request: %s", test.name, err)
+			continue
+		}
+
+		out, err := ParseCertificateRequest(derBytes)
+		if err != nil {
+			t.Errorf("%s: failed to create certificate request: %s", test.name, err)
+			continue
+		}
+
+		err = out.CheckSignature()
+		if err != nil {
+			t.Errorf("%s: failed to check certificate request signature: %s", test.name, err)
+			continue
+		}
+
+		if out.Subject.CommonName != template.Subject.CommonName {
+			t.Errorf("%s: output subject common name and template subject common name don't match", test.name)
+		} else if len(out.Subject.Organization) != len(template.Subject.Organization) {
+			t.Errorf("%s: output subject organisation and template subject organisation don't match", test.name)
+		} else if len(out.DNSNames) != len(template.DNSNames) {
+			t.Errorf("%s: output DNS names and template DNS names don't match", test.name)
+		} else if len(out.EmailAddresses) != len(template.EmailAddresses) {
+			t.Errorf("%s: output email addresses and template email addresses don't match", test.name)
+		} else if len(out.IPAddresses) != len(template.IPAddresses) {
+			t.Errorf("%s: output IP addresses and template IP addresses names don't match", test.name)
+		}
+	}
+}
+
+func parseCIDR(s string) *net.IPNet {
+	_, net, err := net.ParseCIDR(s)
+	if err != nil {
+		panic(err)
+	}
+	return net
+}
+
+func parseURI(s string) *url.URL {
+	uri, err := url.Parse(s)
+	if err != nil {
+		panic(err)
+	}
+	return uri
+}
+
+func TestCreateSelfSignedCertificate(t *testing.T) {
+	random := rand.Reader
+
+	sm2Priv, err := sm2.GenerateKey(rand.Reader)
+	if err != nil {
+		t.Fatalf("Failed to generate SM2 key: %s", err)
+	}
+
+	ecdsaPriv, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	if err != nil {
+		t.Fatalf("Failed to generate ECDSA key: %s", err)
+	}
+
+	ed25519Pub, ed25519Priv, err := ed25519.GenerateKey(random)
+	if err != nil {
+		t.Fatalf("Failed to generate Ed25519 key: %s", err)
+	}
+
+	tests := []struct {
+		name      string
+		pub, priv interface{}
+		checkSig  bool
+		sigAlgo   x509.SignatureAlgorithm
+	}{
+		{"RSA/RSA", &testPrivateKey.PublicKey, testPrivateKey, true, x509.SHA1WithRSA},
+		{"RSA/ECDSA", &testPrivateKey.PublicKey, ecdsaPriv, false, x509.ECDSAWithSHA384},
+		{"RSA/SM2", &testPrivateKey.PublicKey, sm2Priv, false, x509.UnknownSignatureAlgorithm},
+		{"ECDSA/RSA", &ecdsaPriv.PublicKey, testPrivateKey, false, x509.SHA256WithRSA},
+		{"ECDSA/ECDSA", &ecdsaPriv.PublicKey, ecdsaPriv, true, x509.ECDSAWithSHA1},
+		{"ECDSA/SM2", &ecdsaPriv.PublicKey, sm2Priv, false, x509.UnknownSignatureAlgorithm},
+		{"SM2/ECDSA", &sm2Priv.PublicKey, ecdsaPriv, false, x509.ECDSAWithSHA1},
+		{"RSAPSS/RSAPSS", &testPrivateKey.PublicKey, testPrivateKey, true, x509.SHA256WithRSAPSS},
+		{"ECDSA/RSAPSS", &ecdsaPriv.PublicKey, testPrivateKey, false, x509.SHA256WithRSAPSS},
+		{"SM2/RSAPSS", &sm2Priv.PublicKey, testPrivateKey, false, x509.SHA256WithRSAPSS},
+		{"RSAPSS/ECDSA", &testPrivateKey.PublicKey, ecdsaPriv, false, x509.ECDSAWithSHA384},
+		{"Ed25519", ed25519Pub, ed25519Priv, true, x509.PureEd25519},
+		{"SM2", &sm2Priv.PublicKey, sm2Priv, true, x509.UnknownSignatureAlgorithm},
+	}
+
+	testExtKeyUsage := []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth, x509.ExtKeyUsageServerAuth}
+	testUnknownExtKeyUsage := []asn1.ObjectIdentifier{[]int{1, 2, 3}, []int{2, 59, 1}}
+	extraExtensionData := []byte("extra extension")
+
+	for _, test := range tests {
+		commonName := "test.example.com"
+		template := x509.Certificate{
+			// SerialNumber is negative to ensure that negative
+			// values are parsed. This is due to the prevalence of
+			// buggy code that produces certificates with negative
+			// serial numbers.
+			SerialNumber: big.NewInt(-1),
+			Subject: pkix.Name{
+				CommonName:   commonName,
+				Organization: []string{"Σ Acme Co"},
+				Country:      []string{"US"},
+				ExtraNames: []pkix.AttributeTypeAndValue{
+					{
+						Type:  []int{2, 5, 4, 42},
+						Value: "Gopher",
+					},
+					// This should override the Country, above.
+					{
+						Type:  []int{2, 5, 4, 6},
+						Value: "NL",
+					},
+				},
+			},
+			NotBefore: time.Unix(1000, 0),
+			NotAfter:  time.Unix(100000, 0),
+
+			SignatureAlgorithm: test.sigAlgo,
+
+			SubjectKeyId: []byte{1, 2, 3, 4},
+			KeyUsage:     x509.KeyUsageCertSign,
+
+			ExtKeyUsage:        testExtKeyUsage,
+			UnknownExtKeyUsage: testUnknownExtKeyUsage,
+
+			BasicConstraintsValid: true,
+			IsCA:                  true,
+
+			OCSPServer:            []string{"http://ocsp.example.com"},
+			IssuingCertificateURL: []string{"http://crt.example.com/ca1.crt"},
+
+			DNSNames:       []string{"test.example.com"},
+			EmailAddresses: []string{"gopher@golang.org"},
+			IPAddresses:    []net.IP{net.IPv4(127, 0, 0, 1).To4(), net.ParseIP("2001:4860:0:2001::68")},
+			URIs:           []*url.URL{parseURI("https://foo.com/wibble#foo")},
+
+			PolicyIdentifiers:       []asn1.ObjectIdentifier{[]int{1, 2, 3}},
+			PermittedDNSDomains:     []string{".example.com", "example.com"},
+			ExcludedDNSDomains:      []string{"bar.example.com"},
+			PermittedIPRanges:       []*net.IPNet{parseCIDR("192.168.1.1/16"), parseCIDR("1.2.3.4/8")},
+			ExcludedIPRanges:        []*net.IPNet{parseCIDR("2001:db8::/48")},
+			PermittedEmailAddresses: []string{"foo@example.com"},
+			ExcludedEmailAddresses:  []string{".example.com", "example.com"},
+			PermittedURIDomains:     []string{".bar.com", "bar.com"},
+			ExcludedURIDomains:      []string{".bar2.com", "bar2.com"},
+
+			CRLDistributionPoints: []string{"http://crl1.example.com/ca1.crl", "http://crl2.example.com/ca1.crl"},
+
+			ExtraExtensions: []pkix.Extension{
+				{
+					Id:    []int{1, 2, 3, 4},
+					Value: extraExtensionData,
+				},
+				// This extension should override the SubjectKeyId, above.
+				{
+					Id:       oidExtensionSubjectKeyId,
+					Critical: false,
+					Value:    []byte{0x04, 0x04, 4, 3, 2, 1},
+				},
+			},
+		}
+
+		derBytes, err := CreateCertificate(random, &template, &template, test.pub, test.priv)
+		if err != nil {
+			t.Errorf("%s: failed to create certificate: %s", test.name, err)
+			continue
+		}
+
+		cert, err := ParseCertificate(derBytes)
+		if err != nil {
+			t.Errorf("%s: failed to parse certificate: %s", test.name, err)
+			continue
+		}
+
+		if len(cert.PolicyIdentifiers) != 1 || !cert.PolicyIdentifiers[0].Equal(template.PolicyIdentifiers[0]) {
+			t.Errorf("%s: failed to parse policy identifiers: got:%#v want:%#v", test.name, cert.PolicyIdentifiers, template.PolicyIdentifiers)
+		}
+
+		if len(cert.PermittedDNSDomains) != 2 || cert.PermittedDNSDomains[0] != ".example.com" || cert.PermittedDNSDomains[1] != "example.com" {
+			t.Errorf("%s: failed to parse name constraints: %#v", test.name, cert.PermittedDNSDomains)
+		}
+
+		if len(cert.ExcludedDNSDomains) != 1 || cert.ExcludedDNSDomains[0] != "bar.example.com" {
+			t.Errorf("%s: failed to parse name constraint exclusions: %#v", test.name, cert.ExcludedDNSDomains)
+		}
+
+		if len(cert.PermittedIPRanges) != 2 || cert.PermittedIPRanges[0].String() != "192.168.0.0/16" || cert.PermittedIPRanges[1].String() != "1.0.0.0/8" {
+			t.Errorf("%s: failed to parse IP constraints: %#v", test.name, cert.PermittedIPRanges)
+		}
+
+		if len(cert.ExcludedIPRanges) != 1 || cert.ExcludedIPRanges[0].String() != "2001:db8::/48" {
+			t.Errorf("%s: failed to parse IP constraint exclusions: %#v", test.name, cert.ExcludedIPRanges)
+		}
+
+		if len(cert.PermittedEmailAddresses) != 1 || cert.PermittedEmailAddresses[0] != "foo@example.com" {
+			t.Errorf("%s: failed to parse permitted email addreses: %#v", test.name, cert.PermittedEmailAddresses)
+		}
+
+		if len(cert.ExcludedEmailAddresses) != 2 || cert.ExcludedEmailAddresses[0] != ".example.com" || cert.ExcludedEmailAddresses[1] != "example.com" {
+			t.Errorf("%s: failed to parse excluded email addreses: %#v", test.name, cert.ExcludedEmailAddresses)
+		}
+
+		if len(cert.PermittedURIDomains) != 2 || cert.PermittedURIDomains[0] != ".bar.com" || cert.PermittedURIDomains[1] != "bar.com" {
+			t.Errorf("%s: failed to parse permitted URIs: %#v", test.name, cert.PermittedURIDomains)
+		}
+
+		if len(cert.ExcludedURIDomains) != 2 || cert.ExcludedURIDomains[0] != ".bar2.com" || cert.ExcludedURIDomains[1] != "bar2.com" {
+			t.Errorf("%s: failed to parse excluded URIs: %#v", test.name, cert.ExcludedURIDomains)
+		}
+
+		if cert.Subject.CommonName != commonName {
+			t.Errorf("%s: subject wasn't correctly copied from the template. Got %s, want %s", test.name, cert.Subject.CommonName, commonName)
+		}
+
+		if len(cert.Subject.Country) != 1 || cert.Subject.Country[0] != "NL" {
+			t.Errorf("%s: ExtraNames didn't override Country", test.name)
+		}
+
+		for _, ext := range cert.Extensions {
+			if ext.Id.Equal(oidExtensionSubjectAltName) {
+				if ext.Critical {
+					t.Fatal("SAN extension is marked critical")
+				}
+			}
+		}
+
+		found := false
+		for _, atv := range cert.Subject.Names {
+			if atv.Type.Equal([]int{2, 5, 4, 42}) {
+				found = true
+				break
+			}
+		}
+		if !found {
+			t.Errorf("%s: Names didn't contain oid 2.5.4.42 from ExtraNames", test.name)
+		}
+
+		if cert.Issuer.CommonName != commonName {
+			t.Errorf("%s: issuer wasn't correctly copied from the template. Got %s, want %s", test.name, cert.Issuer.CommonName, commonName)
+		}
+
+		if cert.SignatureAlgorithm != test.sigAlgo {
+			t.Errorf("%s: SignatureAlgorithm wasn't copied from template. Got %v, want %v", test.name, cert.SignatureAlgorithm, test.sigAlgo)
+		}
+
+		if !reflect.DeepEqual(cert.ExtKeyUsage, testExtKeyUsage) {
+			t.Errorf("%s: extkeyusage wasn't correctly copied from the template. Got %v, want %v", test.name, cert.ExtKeyUsage, testExtKeyUsage)
+		}
+
+		if !reflect.DeepEqual(cert.UnknownExtKeyUsage, testUnknownExtKeyUsage) {
+			t.Errorf("%s: unknown extkeyusage wasn't correctly copied from the template. Got %v, want %v", test.name, cert.UnknownExtKeyUsage, testUnknownExtKeyUsage)
+		}
+
+		if !reflect.DeepEqual(cert.OCSPServer, template.OCSPServer) {
+			t.Errorf("%s: OCSP servers differ from template. Got %v, want %v", test.name, cert.OCSPServer, template.OCSPServer)
+		}
+
+		if !reflect.DeepEqual(cert.IssuingCertificateURL, template.IssuingCertificateURL) {
+			t.Errorf("%s: Issuing certificate URLs differ from template. Got %v, want %v", test.name, cert.IssuingCertificateURL, template.IssuingCertificateURL)
+		}
+
+		if !reflect.DeepEqual(cert.DNSNames, template.DNSNames) {
+			t.Errorf("%s: SAN DNS names differ from template. Got %v, want %v", test.name, cert.DNSNames, template.DNSNames)
+		}
+
+		if !reflect.DeepEqual(cert.EmailAddresses, template.EmailAddresses) {
+			t.Errorf("%s: SAN emails differ from template. Got %v, want %v", test.name, cert.EmailAddresses, template.EmailAddresses)
+		}
+
+		if len(cert.URIs) != 1 || cert.URIs[0].String() != "https://foo.com/wibble#foo" {
+			t.Errorf("%s: URIs differ from template. Got %v, want %v", test.name, cert.URIs, template.URIs)
+		}
+
+		if !reflect.DeepEqual(cert.IPAddresses, template.IPAddresses) {
+			t.Errorf("%s: SAN IPs differ from template. Got %v, want %v", test.name, cert.IPAddresses, template.IPAddresses)
+		}
+
+		if !reflect.DeepEqual(cert.CRLDistributionPoints, template.CRLDistributionPoints) {
+			t.Errorf("%s: CRL distribution points differ from template. Got %v, want %v", test.name, cert.CRLDistributionPoints, template.CRLDistributionPoints)
+		}
+
+		if !bytes.Equal(cert.SubjectKeyId, []byte{4, 3, 2, 1}) {
+			t.Errorf("%s: ExtraExtensions didn't override SubjectKeyId", test.name)
+		}
+
+		if !bytes.Contains(derBytes, extraExtensionData) {
+			t.Errorf("%s: didn't find extra extension in DER output", test.name)
+		}
+
+		if test.checkSig {
+			err = cert.CheckSignatureFrom(cert)
+			if err != nil {
+				t.Errorf("%s: signature verification failed: %s", test.name, err)
+			}
+		}
+	}
+}
+
+func TestCRLCreation(t *testing.T) {
+	block, _ := pem.Decode([]byte(pemPrivateKey))
+	privRSA, _ := x509.ParsePKCS1PrivateKey(block.Bytes)
+	block, _ = pem.Decode([]byte(pemCertificate))
+	certRSA, _ := ParseCertificate(block.Bytes)
+
+	block, _ = pem.Decode([]byte(ed25519CRLKey))
+	privEd25519, _ := ParsePKCS8PrivateKey(block.Bytes)
+	block, _ = pem.Decode([]byte(ed25519CRLCertificate))
+	certEd25519, _ := ParseCertificate(block.Bytes)
+
+	tests := []struct {
+		name string
+		priv interface{}
+		cert *Certificate
+	}{
+		{"RSA CA", privRSA, certRSA},
+		{"Ed25519 CA", privEd25519, certEd25519},
+	}
+
+	loc := time.FixedZone("Oz/Atlantis", int((2 * time.Hour).Seconds()))
+
+	now := time.Unix(1000, 0).In(loc)
+	nowUTC := now.UTC()
+	expiry := time.Unix(10000, 0)
+
+	revokedCerts := []pkix.RevokedCertificate{
+		{
+			SerialNumber:   big.NewInt(1),
+			RevocationTime: nowUTC,
+		},
+		{
+			SerialNumber: big.NewInt(42),
+			// RevocationTime should be converted to UTC before marshaling.
+			RevocationTime: now,
+		},
+	}
+	expectedCerts := []pkix.RevokedCertificate{
+		{
+			SerialNumber:   big.NewInt(1),
+			RevocationTime: nowUTC,
+		},
+		{
+			SerialNumber:   big.NewInt(42),
+			RevocationTime: nowUTC,
+		},
+	}
+
+	for _, test := range tests {
+		crlBytes, err := test.cert.CreateCRL(rand.Reader, test.priv, revokedCerts, now, expiry)
+		if err != nil {
+			t.Errorf("%s: error creating CRL: %s", test.name, err)
+		}
+
+		parsedCRL, err := x509.ParseDERCRL(crlBytes)
+		if err != nil {
+			t.Errorf("%s: error reparsing CRL: %s", test.name, err)
+		}
+		if !reflect.DeepEqual(parsedCRL.TBSCertList.RevokedCertificates, expectedCerts) {
+			t.Errorf("%s: RevokedCertificates mismatch: got %v; want %v.", test.name,
+				parsedCRL.TBSCertList.RevokedCertificates, expectedCerts)
+		}
+	}
+}